It’s been raining off and on for days. It rained last week during a party, and people were tracking water and a little mud from the driveway runoff onto the porch all afternoon. We had so many different kinds of footprints that it would have made for a great crime scene demonstration.
Because, one of the most overlooked pieces of evidence at a crime scene is created by footwear.
Imagine: If a window breaks as a thief enters the premises during the commission of a burglary, the glass will fall into the house, and onto the floor or rug below the window. When the thief steps through the window, unless the thief has wings, he/she will probably plant a foot right in the middle of the glass. And walk through the house, most likely tracking minute pieces of that glass. That glass may also become embedded in the grooves of the sole of the shoe, creating a distinctive footprint.
If the investigating officer can place a suspect at the scene with the footprint, then there is probable cause to fingerprint that suspect and hopefully establish a link to the crime.
A new method of eliminating suspects right at the scene involves stepping into a tray that contains a pad soaked with harmless clear ink that doesn’t stain, then stepping onto a chemically treated impression card. No messy cleanup, immediate results, and it can even show details of wear and tear on the shoe. This can be a way to establish a known standard (we know where this impression came from) to compare with multiple tread prints at the scene.
Footwear Clear Ink Impression
Another tool for creating a known standard is the foam impression system. It takes a bit longer, (24 hours) but clear, crisp impressions can be made, including of the pebbles and bits stuck deep into the grooves and the writing on the arch. Very helpful when trying to place suspects at the scene. A rock stuck in the sole is a random characteristic that can’t be duplicated, so becomes another point of identification.
This is how it works: Somebody steps into a box of stiff-ish foam – a bit like stepping into wet sand.
An impression is made instantaneously. The detail is great – down to the wear on the heel.
Pre-mixed dental stone (made with distilled water and the powder) is used to fill the impression.
It takes 24 hours for the cast to become firm enough to pop out of the foam. We now have a permanent record of the footwear tread, which could be used for comparison to other prints found at the scene.
Footwear Casts
Occasionally footprints are found on the ground outside a window or in the gardens surrounding a house after a burglary or homicide. Ever see a crime show on TV where the fictional investigator makes a snap judgment about the height and weight of the owner of the footprint because of the depth of the impression? That’s merely a plot device and is not scientific evidence in real life. A crime scene photographer or investigator can photograph the footprint (next to a measurement scale), make a take away cast, and then compare the impression with those of the suspects or other bystanders at the scene. Beware: making a cast of the print destroys the print, so a photograph must be taken before pouring that first drop of dental stone.
Footprints can be found at bloody crime scenes as well. The suspect walks through the blood, tracks it through the house, cleans it up, but the prints are still there, even though not obvious to the naked eye. Blood just doesn’t go away, no matter how hard you try to get rid of it. It seeps into the cracks and crevices of a floor and even behind baseboards.
A savvy investigator will collect sections of carpet (or flooring) taken from where the suspect might have walked during the commission of the crime, then conduct a presumptive test for blood (LCV – Aqueous Leuco Crystal Violet), find a usable footprint, compare it to a known standard, and then be able to place the suspect at the scene.
Be careful where you walk. That footprint can be used as evidence.
TV makes the job of a CSI tech look like a lot of fun.
It looks like an easy job, too. Get a call from dispatch, arrive at a crime scene, pop on the gloves, shine a flashlight around, take a few photos, collect the evidence along with your team of 4-5 colleagues and go back to the lab an hour or so later, ready to process all of it.
Have the real CSI techs and law enforcement professionals stopped laughing yet? 😉
Here’s the reality:
Most small towns (under 50,000 people) have no CSI lab. None. The local police in smaller towns are able to collect fingerprints, but most have to send them off to a State Lab to be processed.
Many towns, even with a population of 100,000 people, don’t have a ballistics lab to check the caliber of any bullets/casings left behind at the scene or found in the victim’s body.
North Carolina (as of 2019) had a population of 10.48 million, and has three State crime labs – one full service and two regional labs.
New York State (as of 2019) had a population of 19.45 million, and has four State crime labs – one full service and three specializing in varied areas.
New Jersey (as of 2019) had a population of 8.88 million. It has five State labs.
Texas (as of 2019) had a population of 28.99 million, with a full service forensic lab in Austin and 14 regional labs, some conducting only drug testing, and others close to full service.
And all of those crime labs are processing evidence from all kinds of crimes (burglary, robbery, rape, arson, cold case, assault, etc.) not just murders. It take a few hours to get the prints, preserve the evidence, bag and tag it for transport, but it takes months to get it processed, because there is a long line of cases ahead of yours. In some States, the wait is as long as 18 months. That is not a typo, folks. Eighteen months to wait until the evidence can be processed. Even if the case is a high profile one, moving to the head of the line might only shorten the wait to 2-3 months, because there are other high profile cases in line as well or cases that are already in court, waiting for clarification of the evidence.
There is no such thing as instantaneous fingerprint matches. See the article about fingerprint analysis here. There are now handheld machines that scan a viable fingerprint at the scene, but that only speeds up the collection process, not the identification of the fingerprint. (I was recently told that a new fingerprint reader can return an answer in 45 seconds, but some fingerprint experts are reserving judgment as to the accuracy of the matches.)
Get the picture? The State Bureaus of Investigation are short-staffed and the cases more numerous, as attorneys seek to prove or disprove beyond the shadow of a doubt that the evidence gathered at the scene linked their clients to the crime.
In general, the analysts examine all types of evidence related to criminal investigations and assist the criminal justice system. They can provide:
Consultation on the value, use, collection, and preservation of evidence,
Analysis and comparison of evidence from crime scenes and/or people,
Expert testimony in court proceedings, and
Assistance for collecting evidence and processing crime scenes,
Forensic science information to law enforcement agencies and district attorneys.
ALL of that evidence must be collected in a thorough and efficient manner by the Crime SceneTechnician or Crime Scene Investigator. Cases are won and lost on how the evidence is handled – both the chain of custody and the collecting of the correct evidence can be factors in how a suspect is perceived.
I had a chance to chat with a CSI who has been in the field for about 10 years. She generously shared information about her day – soooo different from the image of the CSI jobs projected on TV.
She enters a crime scene after a Patrol Officer has cleared the house (made sure that no unauthorized person is in it). A Deputy might walk her through the house, and depending on the crime, the owner of the house then walks her through, pointing out items that might have been disturbed or areas where items are missing. She takes notes during the tours so that she can come up with a Plan of Action – how to process the scene.
In general, she will take photos first, and then collect the evidence. If a homicide is suspected, she might take video as well as still photographs.
She might see patterns of wreckage, or concentration of destruction, or even similarities with other cases, but it is not her job to focus on the M.O. (modus operandi) or narrow her collection efforts based on a hunch. She is there to collect all the evidence.
She might be looking for:
Fingerprints
Blood spatters
Fibers
Footwear impressions
Tire impressions
Tool impressions
DNA samples (hair, nails, blood, saliva, etc)
Murder weapon
Point of entry
Kinds of items taken
What a CSI leaves at the scene is sometimes as important as what he/she collects, so it is vital to be thorough. The detectives and attorneys decide what is significant to the case.
The trunk of a CSIs car is filled with the tools of the trade. They have kits for each type of evidence collection and if they know in general what the scene will call for, they may grab an additional kit from headquarters. They might even carry a tarp to cover the ground (creating a collection place for the evidence) if the scene is outdoors – such as a train wreck.
The CSI I interviewed works in Major Crimes for the Sheriff’s Department, and when she is called to a scene, she works 12-hour shifts, by herself. In most cases, she collects all the evidence, bags and tags it appropriately, and hands it all to the detective in charge. She works 14 days a month, equally divided between the day shift and the night shift. On occasion, a 12-hour shift is not long enough to collect everything at a particular crime scene, so she stays a bit longer to finish. If it looks as if she has to work for another shift, a Patrol Officer will guard the scene until she returns to finish collection on her next shift. If the case merits 24-hour collection (because of weather or the condition of the scene/body) the CSI on the next shift will continue the collection, with any evidence collected up to that point handed over to the new person.
Clear chain of possession of the evidence dictates that in a case where collection goes on for more than one shift, limited people will have keys to the building. There are evidence cards showing who collected it, and anyone entering or leaving the scene will have to sign in and out with the Patrol Officer on duty.
For information about Footwear Evidence, click here.
Next week: The life of a CSI – rewards and challenges.
Continuingthe series of articles about Evidence Collection Training Classes held at SIRCHIE.
Part 4 – “Quick! Grab the glue gun!”
Wet Lift Print as seen on a Comparator
We often hear it said on TV and in the movies that there are items and surfaces that do not hold fingerprints or that fingerprints cannot be recovered from them. On Day #4 of the Sirchie Evidence Collection Training Classes held at the Sirchie Fingerprint Laboratories in NC, we experimented with a variety of surfaces to see what would happen if…
Skin is reported to be one of the most difficult surfaces from which to lift a print, because the prints fade so quickly. But, after three days of dusting and chemically treating and lifting and photographing dubious fingerprints, our group of dogged writer/investigators was not to be deterred.
The set of prints in the photograph below were lifted from an arm. Not clothing, the arm itself. And not by using fingerprint powder on the arm. A classmate kindly offered up her arm to be grabbed. Then a piece of specially treated paper (chromicoat) was pressed onto the area of her arm where the fingerprints were likely to be found. That paper was then dusted with fingerprint powder and the prints popped up. We now knew it was possible to lift the prints if they were minutes old, but we had access to both the specially treated paper and the powder immediately after the grab. We also knew from experience that our grabber always left really good prints on all the surfaces touched during the previous days.
Lift from skin using Chromicoat treated paper
We proposed various scenarios to our instructor (equally curious Robert Skiff, Sirchie Training Manager/Technical Training Specialist). What if a mugger grabbed a bare arm and tried to drag us into an alley? How close would we have to be to the police station after we got away from the mugger in order to get the prints processed? How much time did we have before they faded away? Would the lift work if we used plain paper, since it was highly unlikely that an ordinary gal would be carrying chromicoat paper in a pocket? What if the police station wasn’t close by, therefore no access to fingerprint powder?
The answers were time sensitive. It was possible to lift prints from a bare arm with plain paper, but only if the lift was made during the first few minutes and only if the suspect left a strong sample. It’s possible to use cigarette ashes as a substitute for the fingerprint powder. Conclusions? There were too many variables for this to be a reliable way to catch a crook. Now…if you were grabbed around the corner from a police station OR were a smoker AND the mugger had dirty hands AND you had a clean piece of paper in your pocket AND you had attended this class… Hmmm…maybe in a sci-fi mystery. However, not completely impossible.
Another difficult surface from which to lift prints is the dashboard of a car. Think about it. If you press your hand onto a dashboard, your skin (with all the loops and whorls and arches) is also pressing into the crevices of the pebbled surface. Same thing is true for an orange or a football. A straight gel lift or hinge lifter will not do the job effectively. A tape lift may only pick up the top of the print.
Dashboard surface
But, the investigator sees the possible print and doesn’t want to lose the opportunity to catch the crook. The answer in the past was to dust the likely area with magnetic fingerprint powder, then apply a Blue Glue gel and wait for the gel to cure before lifting it off the dash – about five hours. FIVE hours? The crook is getting away! No time to wait!
These days, the preferred lifting product (after applying the magnetic powder to enhance the print) is a transparent liquid silicone (PVS200 – polyvinyl siloxane), applied with an extruder gun. It flows down into the crevices, dries in six minutes, and gets into every bit of the print. After the polyvinyl dries, it can be lifted, and then placed on a backing card to preserve the print. At that point, it can be placed under an Optical Comparator, photographed, and sent off to AFIS for an ID/comparison.
This epoxy is not good for every surface (it rips paper, etc) but is very good for pitted, bumpy surfaces like alligator skin and dashboards. Gotcha!
Dashboard Lift
Another tricky scenario: The cop is in pursuit of an unidentified car thief or robber and chases him through a parking lot. The cop witnesses the suspect firmly planting his palm on the trunk of a car as he cuts through a tight space. The cop grins as he realizes that even if the guy outruns him, he can catch him through the palm print. And, then, it starts to pour. Does the print get washed away? Or become unusable?
Not if the Field Kit is handy! When forced to do a wet lift, it is possible to use SPR (Small Particle Reagent – finely ground particles suspended in a detergent solution). Spray the print with a fine mist of SPR and let set. Lay the hinge lifter just off the print and place it down carefully, employing a squeegee at the same time, to slowly remove the excess water. This method can be used to develop prints on non-porous surfaces – cans, bottles, windows, and other glossy surfaces, but not on paper or cardboard.
Wet Lift Prints
Criminals who tie their victims up during the commission of a crime frequently use duct tape for the job. That duct tape is almost always full of prints that get embedded into the tape. It’s practically impossible to manipulate and tear the tape while wearing gloves (I tried this once and the gloves got so stuck to the tape that I threw the resulting mess away), so he leaves prints while unrolling and tearing the tape. Even if he has wiped the smooth surface of the tape clean to cover his identity, the sticky side can’t be wiped without taking away the sticky. Balls of tape tossed aside by a suspect have been processed successfully for prints, but first the tape had to be released from itself.
Separating folded duct tape from itself
A 2% chloroform tape release agent is dropped liberally on the area where the two pieces of tape meet. Two people need to work together on this – one person places the drops continuously while the other person pulls the tape apart. The ends of the tape are folded over (about ¼”) and the tape is flattened for 24 hours before further processing.
Adhesive-side developer
After 24 hours, adhesive-side developer is applied to the sticky side of the duct tape, allowed to sit for a few minutes, then rinsed off and voila! The prints are clearly visible, can be photographed, covered with clear tape to protect them, viewed under the Optical Comparator, entered into the system, and sent off to AFIS. (Crystal Violet can also be used for processing this type of print, but is toxic and should only be used in a lab.)
Duct tape prints
AFIS – what is it and does it really help identify a person of interest in a crime?
Anyone who has watched TV crime shows during the last decade has heard the acronym AFIS. It stands for Automated Fingerprint Identification System. In 1924, the FBI started a fingerprint identification system. They fingerprinted several thousand prisoners incarcerated at Leavenworth, and stored their prints on cards.
As of 2012, the system had broadened to include international prints as well, is an electronic database of 70 million, and contains the prints of both law-abiding citizens as well as those of criminals. While newborn babies are printed, their information is usually entered into a local system unless needed in an abduction case. Real estate agents, childcare workers, Federal employees, and people seeking employment with security and law enforcement agencies are fingerprinted as a matter of course now. Depending on the State, the prints are entered into the State AFIS system, and held until needed in the national system. The fingerprints of any person arrested for any level of crime are sent to the State and then on to the national FBI database. The latest FBI version is named IAFIS (I is for Integrated).
Johnny Leonard, a latent fingerprint expert, visited the class in the afternoon to explain what AFIS can and can’t do. He showed us what a fingerprint examiner looks for in every print or partial print he/she sees, using the Henry Fingerprint Classification and Identification method. The average number of minutiae on every complete print is between 100 and 150. There are distinct ridge patterns to look for in a print: arches, loops and whorls.
Fingerprint Loops
65% of all fingerprint patterns are loops,
Fingerprint Whorls
30% are whorls,
Fingerprint Arches
and only 5% of fingerprint patterns are arches.
Thumb prints are the prints most often left at a crime scene, because people use their thumbs for leverage when pushing through doors or opening safes, or grabbing those golf clubs to use as weapons, etc.
Identifying 8-12 points of similarity between an unknown latent print found at a crime scene and one in the AFIS database is the standard for declaring a match, but some jurisdictions want more for absolute certainty. An examiner plots the print in question for distinct characteristics, makes notes to that effect before sending the print off and waits. AFIS & IAFIS return a list (sometimes as many as 30) of possible matches. At this point, the examiner reviews the possibles and chooses the best match in his/her opinion. And, it might not be the first on the list. Then, another examiner verifies the possible match. There is no such thing as an instantaneous match with just one print from the AFIS or IAFIS databases. TV tells us otherwise, but sorry, that’s merely for dramatic effect.
Other interesting fingerprint details:
*We know that no two people can have the same fingerprints, but not even the same person’s prints are identical.
*Some people have all three types of ridge patterns on one finger.
*Only positive matches from the state AFIS are verified by examiners; not the negative ones.
*Palm prints are now in the AFIS database.
*AFIS looks for change of direction in the whorls, loops, and arches in order to find a match.
*There has not been a case yet where the DNA has not matched the fingerprints at the scene.
The photo below shows a positive match between a latent print and one in the database. The latent is on the left. The database print is on the right. This match placed the suspect at the scene and along with other evidence, resulted in a conviction.
AFIS match
Having been through four days of training, working with prints on a variety of surfaces, we felt confident that we were up to the challenge of matching a few fingerprints on our own. Mr. Leonard showed us 16 pairs of prints and gave us 15 minutes to make decisions. We looked for cluster highlights, tented arches, spots, bifurcations and other techy details. Guess what? The lines began to blur, and not all of us correctly identified all the matches.
TV makes it look easy, with a click and a less than five-minute response time from IAFIS. Not possible, with 70 million fingerprints to choose from. This is not an easy job, even with the new digital readers that speed up the process of finding likely matches at the scene.
Click here for Part 1 – “Have you been fingerprinted?”
Click here for Part 2 – “Where are the Evidence Collection kits made?”
Click here for Part 3 – “Can’t get rid of the blood?”
*Photos taken by Patti Phillips at SIRCHIE Education Training Center in Youngsville, NC.
