(NewsNation) — The four University of Idaho students who were murdered reportedly had their hands bagged at the murder scene to preserve possible DNA evidence.

Forensic expert Joseph Scott Morgan told NewsNation’s “Banfield” that it’s common for perpetrators to unknowingly leave behind hair strands on the victims’ hands. The killer’s skin cells can also become embedded under the nails of their victim.

“Many times, that (hair) contacts onto the surface of the hands because the hands are spattered with blood if you think how sticky blood is, Morgan said. “The perpetrator is not even aware that they’ve left their hair behind. That happens many times.”

If the perpetrator happened to be wearing a ski mask, certain fibers could also stick to the victim.

“It’s quite fascinating … things that can be collected from hands. We do nail scrapings after the bags are removed. And we also do nail trimmings, but the bags are set aside and kept separately. And then all of the items that are contained in there that fall off and transport are preserved, and that’s very important,” Morgan added.

Watch the full interview in the video above.