Forensics Q&A: Fingerprinting

By Kristy Lahoda | @KristyLahoda

Disclaimer: The information provided in this post should not be used for malicious intent unless it is in the form of crime writing. The author is an explosives expert, not an expert in fingerprint analysis. 

QUESTION:  In my novel the protagonist is at a crime scene where fingerprints are found. What are some ways the fingerprints would be readied for analysis and what are some technical bits I can use to make it sound more authentic?

ANSWER: Fingerprints are analyzed by physical or chemical methods.

Types of Fingerprint Evidence

There are three types of prints that can be found at a crime scene: patent, impressions, and latent. Patent prints are those visible prints left as a result of contact with items such as dirt, blood, oil, and grease. Impressions are three-dimensional prints left in soft surfaces such as silly putty, tar, and butter. Latent prints require processing in order to be visible and will be our focus.

Latent Print Residue Composition

Our fingertips have skin called friction ridges that secrete sweat through pores. The composition of this sweat actually forms the latent print as well as any variety of materials that are on the friction ridges.

Latent Print Development

There are two types of methods for print development: physical and chemical methods. The methods used are primarily dependent on the surface the print is found on. The primary physical method is powder dusting. In this method, the powder adheres to the residue allowing for print visualization. Afterward, a piece of transparent lifting tape is applied to the powered print and then mounted onto a background that contrasts with the color of the print powder. Speaking from the limited experience I had during my training in fingerprints, dusting and lifting are art forms. Both procedures require patience and a great deal of skill. The prints can easily be damaged and you are out of luck if only one print is found and it is damaged during processing. Another physical method involves magnetic powder. It has magnetic properties and sticks to a wand. Since there are no brush bristles, the risk of damage to the print is reduced. This method is really cool, but again, I found that it requires technique.

There are several chemical methods. The chemical method that we use often in the crime lab is cyanoacrylate fuming, otherwise known as superglue fuming. The chemical name of superglue is alkyl-2-cyanoacrylate ester. The fumes interact with the latent print residue by polymerizing (i.e., the process of many small molecules combining). We place the item containing the print or prints into a chamber. We place a small dish of superglue in the chamber. The chamber is kept at a certain relative humidity and heat is used as a catalyst (i.e., to speed up the process of the reaction). There are several nice things about superglue fuming. It is an easy procedure, but it also allows for further processing if necessary. The print can be treated with a dye stain that induces fluorescence or luminescence when an alternate light source (ALS) or a laser illuminates the print at a specific wavelength. Examples of two dye stains that the crime lab uses are ardrox and Rhodamine-6G. Another common chemical process is called ninhydrin and is useful for porous surfaces. Ninhydrin reacts with components from the ridge lines containing amino acids. It is commonly applied by spraying, painting, or dipping. The process is slow, but like the superglue process, it can be sped up by adding heat in humid atmosphere. The ninhydrin develops bluish-purple prints. An analog of ninhydrin is 1,8-diazafluorenone (DFO). Ninhydrin and DFO react with components in the latent print residue that are water soluble. A follow-up treatment to ninhydrin and DFO is called physical developer (PD). PD is often used as a follow-up method because it reacts with components in the residue that have not already reacted—water-insoluble components such as lipids. It involves a process based on silver deposition onto the latent print residue.

There are many other chemical methods that can be used. I highlight a few of the more common methods here. The important takeaway is that even though it may seem to be an easy job, it takes a skilled crime scene technician or lab analyst to nondestructively lift the prints.

Kristy Lahoda, Ph.D., is an explosives analyst contractor in a crime lab as well as a technical editor for a scientific journals publishing company.  She writes Christian forensic suspense and discusses forensics on her blog called Explosive Faith.  You can follow her on Facebook and Twitter.

If you have a forensics question for Dr. Lahoda that you'd like to see answered on the QueryTracker Blog, send your question via Carolyn Kaufman using the email link under Contact Us in the right-hand column of the main QTB page.

Making Your Dreams Your Reality Part II

By Kristy Lahoda | @KristyLahoda

So, I left off in the last post encouraging you to find your dreams and to incorporate them into your reality. Now the question becomes, How is this done realistically when it’s not part of your nine-to-five job? 

Despite only having forty pages of my novel written before my twins were born, I was proud of what I had accomplished. It seemed like a good start, but when I would tell people that I was writing a novel and how much I had written, very few people seemed impressed. I want to encourage you to not become disheartened by the lack of support by other people—often it will just serve to discourage and distract you. So how do you write with an extremely busy schedule, despite lack of understanding and encouragement—against the odds?

Be deliberate. After my twins were born, they were in the neonatal intensive care unit (NICU) for six and a half weeks. I was on maternity leave with no obligations at home. It was the perfect time to write, but I was emotionally drained. A phrase familiar to NICU families is “two steps forward, one step back” and we lived that for a month and a half. During that time I reflected on my novel and how I was going to use my maternity leave to accomplish as much as possible while taking care of and enjoying the twins. I set a goal. I decided that once the babies were home, I would take advantage of my maternity leave and write because I might not ever have that much time off of work again. And I did. They came home at the beginning of October and while they slept 18 hours a day, I wrote. I had to be very conscientious about not getting distracted with other things that weren’t as important, but I was moving along quickly enough that my husband challenged me to get to 100 pages by New Year’s Day. I accepted his challenge and suddenly I had a third of my novel written. 

Once I went back to work it took eleven months to finish my novel. The only time I had available to write was in the evening hours after the twins were in bed and during naptime on the weekends. However, I still thought about the novel while I wasn’t writing. When busy doing something that didn’t take a lot of concentration, I would use that time to plan scenes in my novel. I usually knew what I wanted to have happen in the next scene, so I would dwell upon certain questions: How could the characters accomplish what I needed them to do? What did I need to research for the next scene? And so on. This time was invaluable. I highly recommend planning while you are busy doing anything that doesn’t involve much of your mental faculties.

Writing involves sacrifice, as does any other worthwhile endeavor. I wrote not only because I wanted to accomplish an important goal in my life, but also with the hope that there would be a day when I could write professionally at least part-time. I still don’t know if that is going to happen, but I chose to sacrifice the time then for a potentially better future for my family. Was it worth it? I believe it was, but balance is the key. Even though my writing took away quality time from my husband, not to mention cuddle time with my twin babies, my husband was very supportive because he saw that spark in me that he hadn’t seen in a long time. He knew that while I was writing, I was fulfilling an innate desire. Without his encouragement and support, it would not have been worth it. 

Decide whether your writing goals will be detrimental—especially to your family. Do the pros outweigh the cons of your sacrifice? If you have personal time available and you feel a drive to write, then spend some of your free time writing each week. It doesn’t have to be a lot. The important thing is to be consistent, but not militant. Keeping a word or page count per day, even if you don’t write every day, works for many writers. If you feel that you are not spending enough time with your family or doing other things, take the day off from writing and spend your day doing something else. Chances are, it will refresh you and it might give you the inspiration that you need to continue pursuing your dream.

Kristy Lahoda, Ph.D., is an explosives analyst contractor in a crime lab as well as a science content editor for a major educational publishing company.  She writes Christian forensic suspense and discusses forensics on her blog called Explosive Faith.  You can follow her on Facebook and Twitter.

If you have a forensics question for Dr. Lahoda that you'd like to see answered on the QueryTracker Blog, send your question via Carolyn Kaufman using the email link under Contact Us in the right-hand column of the main QTB page.

Making Your Dreams Your Reality

By Kristy Lahoda | @KristyLahoda

I’ve had a lot of dreams since I was young, and at first glance, one might say I have failed to fulfill them. In fact, there are days when I almost convince myself that this is true. Thankfully, those days are few and far between.

Though my life hasn’t turned out exactly the way I envisioned it, in a way, I believe I have fulfilled every memorable dream I had in childhood. I remember sitting in the hallway during church services when I was young and writing books during the sermons. I wanted to be an author. Next, I wanted to be an architect.

By late elementary school, my best friend and I were pretending that we were detectives and forensic chemists and making up “secret” mixtures. Fast forward to high school, when I absolutely loved chemistry. It was during those years that I became fascinated with explosives. In college, I majored in chemistry and decided I wanted to be a forensic scientist. This was before forensic science was on the general public’s radar—before CSI Las Vegas aired. I graduated and was offered a job at a private forensic lab and turned it down. Was this a mistake? Mostly, yes. But, a lot of good things came out of my choice.

I decided that I didn’t know anything about forensics or analytical chemistry and that I should go to grad school and learn before working in a crime lab. Knowing what I know now, nothing trumps experience. I was fortunate enough, however, to do my research for a professor who had worked at the FBI as an explosives researcher. It was a perfect fit for me. Another really good thing to come out of my decision to go to grad school was meeting my future husband the last year I was there!

I also got the itch to start writing a forensic crime novel, but only wrote about twenty pages. I never had a plot and thought that things would just come to me as I wrote. I didn’t spend much time writing, so I didn’t get anywhere. After a short post-doctoral stint, I hoped that I would be able to get a job in the explosives field. Nothing. In fact, I was unemployed for almost two years. While unemployed, I began to get the itch to write a book again.

I did profuse amounts of research and filled up several notebooks. I came up with ideas, talked them over with my husband, and we brainstormed together. I had a plot and an outline of the first fifteen chapters and an idea of how I wanted the ending to turn out. Just after I wrote the Prologue, I was offered a job as a science content editor at a major educational publishing company.

Over three years later, I have yet to work full-time in the forensic field, but is that stopping me from finding fulfillment? Does that mean that I can’t still enjoy forensics? Of course not! I’ll let you in on a few nuggets I’ve learned along the way.

First, don’t give up on your dreams! Second, sometimes you just have to get creative. You never know when an opportunity will present itself. Third, there are many avenues for achieving similar goals—this is where creativity comes into play. Professionally, editing never entered my mind, but after being unemployed for so long, I got creative in my job search. I realized that being a science content editor combined my interest in writing with science. A year and a half ago, I got the opportunity to be an explosives analyst contractor for a crime lab. This has greatly enhanced my writing—it comes straight from the source, not just what I imagine working in a crime lab to be like. Living what you are writing about goes a long way with agents.

I have found a way to incorporate the different things I wanted to be growing up with the reality of not always getting to do what I wanted or what I envisioned my life to be like as a grown up. I wanted to be an author, architect, detective, and a forensic explosives chemist. In reality, I am a full-time editor and an explosives contractor, who has found a way to combine my passions—I am the architect, or writer if you will, of forensic explosives suspense. I want to encourage you to find a way to incorporate your dreams into your life.

Are your dreams long forgotten? If so, find them! What are you passionate about? What do you enjoy doing? Take away your obligations and/or money limitations for a moment. If you could do anything, what would you do?

Now, is there a way to incorporate your dreams into reality? Are you unemployed? Make good use of your spare time. When you aren’t looking for employment, which admittedly can be a full-time job in and of itself, start working on things you’ve been meaning to do. Maybe you haven’t had the opportunity to live out or experience your dreams in the way you were hoping. Since you are a writer, maybe this can be through writing…or maybe there is another avenue that you haven’t yet thought of! I am here to tell you that you can use the gifts and talents you’ve been given despite your restrictions, you just may have to get creative.

Kristy Lahoda, Ph.D., is an explosives analyst contractor in a crime lab as well as a science content editor for a major educational publishing company.  She writes Christian forensic suspense and discusses forensics on her blog called Explosive Faith.  You can follow her on Facebook and Twitter.

If you have a forensics question for Dr. Lahoda that you'd like to see answered on the QueryTracker Blog, send your question via Carolyn Kaufman using the email link under Contact Us in the right-hand column of the main QTB page.

Forensics Q&A: Explosives Crime Scene Investigation

By Kristy Lahoda | @KristyLahoda

Disclaimer: The information provided in this post should not be used for malicious intent unless it is in the form of crime writing. The author is an explosives expert, not a crime scene expert. While every attempt was made to ensure the accuracy of this information, for security purposes, some details may have been withheld.

QUESTION: My antagonist is a juvenile delinquent who set off a pipe bomb with the intent to destroy property. What would the bomb scene investigation look like?


ANSWER: There should be three phases of the investigation: outside investigation, control and coordination, and inside investigation.

Outside Investigation

First responders have the initial responsibility. Above all else, safety and security must be ensured. After assessment, a call for backup may be warranted. If the scene is unsafe, the first responder must not only wait until the scene is made safe, but must also ensure that the scene is secure for the safety of others. The last casualty from the bombing of the Alfred P. Murrah federal building in Oklahoma City was a nurse who wanted to help the injured. She passed away because a computer monitor fell on her from one of the compromised floors above. Once the scene is safe, rescue of victims is performed.

The crime scene must be secured. This involves establishing an inner security perimeter by placing crime scene tape around the scene. Hazards should be identified and removed or mitigated. Sometimes it is not initially known if the explosion was the result of a bomb, so a call to the bomb squad might be necessary in order to check for secondary devices. A structural engineer may need to be called to check the structural integrity. Other potential hazards that must be taken into account may include fire, hazardous materials such as asbestos and carbon monoxide, utilities such as electrical, natural gas, and ruptured water pipes, debris such as metal and glass, and blood-borne pathogens. If there is fire at the bomb scene, firefighters should use only enough water to quench the fire because the evidence could be washed away. Also during this phase the first responders should ensure that evidence that might be removed from the scene is properly preserved. Witnesses should be located and interviewed and license plates checked—the perpetrator might be among the crowd. The outside investigation is not just a phase of the crime scene investigation, but remains ongoing until the case is solved.

Control and Coordination

Control and coordination takes place once the scene is secure. This phase involves compiling the information obtained from the outside investigation and making it available to the inside investigation. The people operating in this capacity direct investigative endeavors by acting as the filter for incoming and outgoing information by briefing and debriefing. They are responsible for resources acquisition and allocation. A command post is set up near the crime scene, but at a distance so as to not interfere.

Inside Investigation

The inside investigation may occur within a building or outside. The term “inside” is used to indicate that this phase of the investigation is generally confined to the crime scene itself. It is like piecing a puzzle together by collecting physical evidence. The inside phase may need to be moved to a secure area if, for example, the structure is unstable.

The crime scene investigator should meet with the first responders at the command post to learn what actions have been taken. Are there are any victims? Is there any relevant information from witnesses regarding the scene? Are there any known hazardous materials present? Is there any physical evidence already located? They should establish perimeters. The inner perimeter should encompass the blast area including where the evidence is present. The command post should be set up at this boundary and should be determined by multiplying 1.5 by the distance from the epicenter to the farthest piece of evidence located. The outer perimeter is the distance at which investigators want to keep people away not affiliated with the crime scene.

The investigator needs to conduct a walkthrough for observation purposes to identify the “nature of the explosion” and possible evidentiary items. The process of documenting the scene may commence during this stage.

After the walkthrough the team lead should come up with an investigative plan for the scene such as contamination prevention. Contamination of the scene with trace evidence is a real possibility. The investigators should wear Tyvek or laundered clothes and shoe coverings. Care should be taken to avoid stepping on potential evidence and destroying things like shoeprints, tire treads, etc.

The team lead should brief the team and assign specific tasks, ensure that team members are wearing proper protective clothing, and provide reminders not to forget the basics—to be on the lookout for fingerprints, shoeprints, tire treads, tool marks, and trace evidence such as DNA, blood, fibers, suspicious packaging and wrappers, etc. A member should be assigned to swab explosive residue.

A number of steps take place during the inside investigation including establishment of a team lead, evidence identification, documentation, collection, and preservation, and the performance of a final survey.

Establishing a Team Lead

A team lead should be chosen to serve as a liaison between the inside investigation unit and the command post, to formulate an action plan such as assigning investigators/scientists to certain tasks in order to cover all bases, arrange for the command post to obtain essential equipment, and help to maintain the morale of the unit. Two essential questions should be asked. What happened? How did it happen? This is the objective of the crime scene search.

Documentation, Identification, Collection, and Preservation

The scene is documented. This includes photographs, sketches, and notes. Photographs of the scene should be taken to include an overall perspective. Once evidence is identified, such as pieces of an explosives device: the possible container, fuzing mechanism, and filler, it may also be documented. Key evidentiary pieces should be photographed individually. The photographer should coordinate with the sketch artist. Photographs of every individual item are not required, but should be taken prior to moving the evidence if that piece is considered vital to the investigation. Evidence custodians collect, package, and label the package. Chain of custody is important during this step, thus an evidence log should be maintained.

Final Survey

A final walkthrough of the crime scene is performed to verify completion of crime scene evidence search, documentation, and processing. Recovery of all equipment used should also be completed at this time.

There are multiple investigations occurring during an explosives crime scene investigation. The outside investigation and inside investigation are linked together through the control and coordination unit. This connection is important to bring the puzzle pieces together for both phases. It is the responsibility of the inside investigative team lead to keep up the team morale due to the nature and tedium of the investigation. This is one of the most important jobs. When the crime scene investigative team grows weary or emotionally unstable, mistakes are made.

Source: Thurman, James T. Practical Bomb Scene Investigation. Boca Raton: CRC Press, Taylor & Francis Group, 2006. 

For more information on these topics, stay tuned for the installments in the upcoming months of Forensics Q&A!

Kristy Lahoda, Ph.D., is an explosives analyst contractor in a crime lab as well as a science content editor for a major educational publishing company.  She writes Christian forensic suspense and discusses forensics on her blog called Explosive Faith.  You can follow her on Facebook and Twitter.

If you have a forensics question for Dr. Lahoda that you'd like to see answered on the QueryTracker Blog, send your question via Carolyn Kaufman using the email link under Contact Us in the right-hand column of the main QTB page.

Forensics Q&A: Not All Explosives Are Created Equal

By Kristy Lahoda | @KristyLahoda

Disclaimer: The information provided in this post should not be used for malicious intent unless it is in the form of crime writing. The author is an explosives expert, not a crime scene expert. While every attempt was made to ensure the accuracy of this information, for security purposes, some details may have been withheld.

QUESTION: I am writing a thriller and my antagonist is planning to make a pipe bomb.  Does it matter what type of explosives she uses?  For example, could something like TNT be used as an explosive in the pipe?

ANSWER: It does matter as not all explosives are created equal.  TNT is not an explosive typically used in a pipe bomb—it does not need to be contained to cause mass destruction.  Explosives are generally grouped into two categories: low explosives (LEs) and high explosives (HEs).  These are differentiated based on the speed of explosion.  LEs deflagrate, HEs detonate.

High Explosives (HEs)

Detonation occurs when the reaction front propagates (i.e the reaction proceeds) through the explosive at a speed greater than the speed of sound,  Detonation occurs at velocities above 3,300 ft/sec (2,250 mph).  For detonation to occur, the assistance of a primary explosive is required.  To provide sufficient energy for the high explosive to begin its energetic decomposition (i.e. the breakdown into chemical components as a result of the energy of the reaction), only small amounts of the primary explosive are needed because they are reactive to shock, friction, or heat.  Detonation results in a rapid release of energy and an accompanying shock wave.

Types of HEs

High explosives are categorized as primary or secondary based on ease of initiation.  When comparing the two, primary explosives are more sensitive to heat, friction, and shock and have less energy, and therefore less power, than secondary explosives.  Secondary explosives are less sensitive to heat, friction, and shock and are more powerful.  Primary explosives are used in detonators and initiation systems.  They can be used to ignite secondary explosives.  Secondary explosives are used in large quantities relative to the primary explosive and are typically used as the main charge.

Primary Explosives

Two common initiating explosives include lead azide and lead styphnate.  Lead azide is very sensitive to initiation by friction, heat, or shock.  The velocity of detonation for lead azide is around 17,500 feet per second.  That’s just over 11,900 miles per hour!  Lead styphnate is sensitive to static electricity and fire, but is less sensitive than lead azide to friction and shock.  Its velocity of detonation is similar to that of lead azide.

Secondary Explosives

Trinitrotoluene (TNT) is one of the most universally known HEs.  Cyclotrimethylene trinitramine (RDX) and pentaerythritol tetranitrate (PETN) are two favorites of terrorists.  In fact, PETN was the explosive that Richard Reid, aka The Shoe Bomber, had concealed in his shoe in an attempt to blow up American Airlines Flight 63.  Another example of a high explosive is ammonium nitrate-fuel oil (ANFO, used by Timothy McVeigh and Terry Nichols in the bombing of the Alfred P. Murrah federal building in Oklahoma City in 1995.

Low Explosives (LEs)

Low explosives are propellants that burn in open air, but deflagrate (burn rapidly) when initiated in confinement.  LEs might not sound that dangerous since they burn, but they can be extremely perilous when used improperly.  In fact, they can even “act” as high explosives upon deflagration given the proper conditions when initiated, such as containment.  Simply stated, deflagration = explosion when confined.  When the LE deflagrates, the burn is faster than in open air.  However, it does not burn as rapidly as detonation occurs.  The reaction front propagates through the low explosive at a velocity less than the speed of sound.  As a result, low explosive deflagration reactions occur at a lower reaction front pressure, velocity, and temperature than HEs.  

Types of LEs

There has been a strong emphasis in counterterrorism literature on high explosives analysis, but the majority of incidents in the US have been due to LEs such as black powder, smokeless powder, improvised explosives, and fireworks. These are the types of explosives that are used in pipe bombs.

In summary, low explosives require containment to deflagrate.  High explosives require primary explosives to initiate detonation of secondary explosives, but are destructive without containment.  After an explosion, there are a number of law enforcement activities that are launched at the crime scene and crime lab including an investigation, a crime scene search, evidence collection, sample preparation, and forensic analysis on the decomposition products of the explosives—called post-blast residue analysis.  The wealth of forensic information obtained post-blast is amazing and should give pause to anyone considering bomb construction.  

For more information on these topics, stay tuned for the installments in the upcoming months of Forensics Q&A.

Kristy Lahoda, Ph.D., is an explosives analyst contractor in a crime lab as well as a science content editor for a major educational publishing company.  She writes Christian forensic suspense and discusses forensics on her blog called Explosive Faith.  You can follow her on Facebook and Twitter.

If you have a forensics question for Dr. Lahoda that you'd like to see answered on the QueryTracker Blog, send your question via Carolyn Kaufman using the email link under Contact Us in the right-hand column of the main QTB page.