When Eugene questions the witness, he mentions his address as 1634 Racine. This is the same address as Malone (Sean Connery) in the Untouchables.
Moto says "Mother pus bucket" which was first said by Peter Venkman (Bill Murray) in Ghostbusters (1984)
While his board was mostly made up of building schematics and sketches of people, Eugene also included one personal detail. He pinned a rolled-out piece of waffle cone to the board above Stephanie's missing poster.
Eugene says "strike that, reverse that", which is similar to what Gene Wilder's character says ("strike that, reverse it") in Willy Wonka & the Chocolate Factory (1971).