Criminals that 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 the crook 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.
What to do? Drop lots of a 2% chloroform tape release agent 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 should then be folded over (about ¼”) and the tape flattened for 24 hours before doing anything else to it.
After 24 hours, adhesive-side developer should be applied to the sticky side of the duct tape, allowed to sit for a few minutes, then rinsed off. The prints are clearly visible, can be photographed, covered with clear tape to protect them, viewed under an Optical Comparator, entered into the system, and sent off to AFIS.
Dashboard prints:
Up until recently, we could not collect decent prints from the dashboard of a getaway car in a reasonable length of time. Most car and truck dashboards have a slightly bumpy surface, more or less because it’s a selling point to non-criminal types – supposedly the pebbled surfaces mean no more pesky fingerprints to clean off if you’re a mom transporting kids after school. Sheila says the juice spills just get buried in the grooves.
But, it’s a potential fingerprint heaven for the CSIs who need to process the abandoned bank heist car. Think about it. If you press your hand onto a dashboard, your skin (with all the loops and whorls and arches and oils) is also pressing into the crevices of the pebbled surface. The problem is that a straight gel lift or hinge lifter will not pick up the prints effectively or may only pick up the top of the print.
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!
Planning to become a crime scene investigator? Then remember to collect the balls of duct tape tossed on the floor or in the garbage cans at the crime scene. Almost definitely, a great source for prints. And don’t forget your extruder gun!
*Photos taken by Patti Phillips at the Sirchie Education and Training facility in Youngsville, NC.
For more information about Sirchie and its products for the law enforcement community, please visit www.Sirchie.com.
I’m reading this, Patti, and wondering how people figure out how to do this. Amazing!
Sue, the guys/gals at the Sirchie Training center said that they spend part of every day experimenting with different ways to use the chemicals, apply the results to investigations, and even come up with new products. Amazing place and people.