My friend had his bike stolen in September, and it just showed up again today. How do we go about getting it back?

I saw the bike and I was being a moron, didn't take pictures or sit with it. I was kind of in a hurry and walked away. My friend saw the guy riding the bike back to his room in the building next door, but we can not go in and get it back. Is there any legal process we could do to coax him out, other than to just wait for him to ride by on it? I live on a college campus, and the campus police said they can't enter a property on suspicion without a reasonable bit of evidence.