"Looks like the killer spent significant time at Ponycon 2017."
The first recorded instance of glitter being used as trace evidence happened at the end of the Cold War in Germany, when the U.S. Army's crime lab used it to solve a sexual assault case during a local celebration. Specific glitter from the victims' Mardi-Gras-like costumes was found on the clothing of the suspects. Another time, a killer in Alaska was nabbed in part because his estranged wife had dropped glitter in his car at some point, and some of it stuck to his victim. More recently, this method was used to bust a deadly hit and run driver who denied being at the wheel, but had a hard time explaining how the exact same cosmetic glitter she wore on her face wound up plastered to the airbag.
It's yet one more example of how, unless you wrap yourself in cellophane / coat yourself in lacquer in preparation for your malfeasance, there's always going to be something left behind that detectives will capitalize on to send your silly novelty-toenail-polish-loving ass up the river.