As the Craigslist Killer assaulted, bound, and robbed his first victim, Las Vegas-area escort, Trisha Leffler, he paused for an odd bit of side business. Philip Markoff leaned over and snatched up the sex worker's panties, Leffler later recalling to CBS News' "48 Hours Mystery" reporter Peter Van Sant, "If he would've looked at my face, it would've been, like, 'What the hell are you doing?'"

Markoff had all the signs of a sex offender, according to Boston Police Commissioner Edward Davis in the "Reelz" documentary series "Murder Made Me Famous" (via People). Markoff might not have sexually assaulted his victims, but in his short crime spree, the behavior was escalating. "He took the underwear of his victims," Davis confirmed to producers, "and saved them to remember the victims."

When police eventually searched Markoff's apartment they found a trove of evidence including bullets matching his murder victim Julissa Brisman, plastic zip ties that also matched, duct tape, fragments of incriminating digital communication, and burner phones, according to Thoughtco. But more relevant to the possible sexual nature of these crimes, hidden under Markoff's mattress, police found 16 pairs of women's panties, some carefully rolled inside of socks. Neither the socks nor the entire trove of women's underwear could be traced to the existing crime spree. This led investigators to wonder if there were yet more unidentified victims — a mystery that remains unresolved.

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