I haven't seen this hit the news or social media yet and I know a lot of Michigan fans like myself get much of their Ann Arbor news from this site, so I thought I would send the community an update in case anyone is looking for more information.
I work on Campus near the corner of State Street and North University. Around 930 PM I heard a large boom from my office. It didn't sound like a gunshot at first, but within about a minute 3 police cars pulled up having traveled fast and with full lights and sirens on display. I could hear officers instructing someone across the street to get on the floor, and though my view was obscured, I do believe this might have been a "guns drawn" type circumstance. Within another 60 seconds another 4 to 5 police cars arrived on the seen, later followed by two ambulances. The entire section of North University between State Street and Fletcher was taped off for a period of time and only emergency vehicles were let through.
Whatever the incident was, it seemed like it was resolved very quickly because after about 20 minutes about half of the police presence left. As I write this I know vehicles are still on the scene.
I'm not sharing this to rubberneck or swirl speculation, but again I get much of my Ann Arbor news from this site and thought I would share in case others are seeking information about what happened this evening.