“A man without duct tape is not a man at all”
Plato 465 BC. Alright, alright, that was my quote but it seems to be the reigning philosophy among those of us afflicted with the Y Chromosome. I dare say you’d be hard pressed to find a tool relied upon by NASA astronauts and DIYers alike. Criminals love it too. You can bind and gag victims, make an improvised grip on a cut down shotgun stock, hold explosives together, or hold the bumper together on your getaway vehicle. Seriously though, criminals utilize everyday items in the commission of crimes and duct tape is no exception. And it’s not just duct tape, any kind of adhesive tape or label can be processed for fingerprints. It may be an address label or stamp on an envelope containing a threatening letter, the sticky edge of a post-it note, cellophane tape sealing an envelope or packing tape sealing a box.
By it’s very nature of being sticky, the adhesive side of tape is a terrific receiving surface for latent fingerprints. The first step is getting the tape separated from whatever surface it’s adhering to. Sometimes you luck out and the threatening letter is taped to the clean smooth glass of the victim’s car. Usually it’s more complicated than that. Duct tape stuck together (sticky side to sticky side) is the worst! That’s because the adhesive tends to stick together so well you simply can’t get the “original” sticky surface containing the print separated cleanly.
Criminalists have tried all kinds of methods from freezing the tape to chemical separators but neither method works consistently well. Exposed areas of the adhesive side are usually the best bet. Also, duct tape may tear off fingertip portions of the latex gloves the suspect was wearing, giving another surface to process. Cellophane and packing tapes, labels, stickers, and stamps usually yield better results. Many criminalists utilize commercial tape separating products like Un-Do to remove the tape from whatever it’s sticking to. These products work very well in preserving the latent fingerprint.
Two of the most common methods used by criminalists are “sticky-side powders” and Gentian Violet (Crystal Violet). Sticky-side powders are mixed with water and Photo-flo 200 to make a paste that is “painted” onto the sticky surface and allowed to stand for 15-30 sec. before being rinsed under a gentle stream of water. Gentian Violet is a dye stain in which the tape is immersed and soaked for up to several minutes and then rinsed with a gentle stream of water or water bath. Both methods work well and often an examiner will select a method that will provide the best contrast with the color of the tape. Gentian Violet turns the fingerprint ridges purple while the Sticky-side powder turns them a light grey.