The prime suspect is none other than Balthazar McSnively, a notorious donut thief with a history of pastel-colored pastry crimes.
We have reason to believe that McSnively was in the vicinity of the crime scene during the time of the heist, and was last seen fleeing with a trail of sprinkles leading out of the alley.
Donut: 1x Boston Creme-filled Fingerprint: Balthazar McSnively (probable match) Sprinkle trail: 10ft, leading to abandoned dumpster behind "Eddie's Donut Shop"
Case still open, but we're getting close. Next step: Forensic Analysis of Sprinkle Trail.