I've got a stranger's bike
I called the police and had them dispatch an ambulance. The folks already involved were taking care of him (including one doctor) physically and staying with him. I offered to take his bike and helmet and keep them safe while he was going to the hospital and whatever else followed so he wouldn't have to worry about his stuff. I gave him my contact information, but was in a rush and left once I saw the ambulance approaching. I haven't heard from him and am getting a wee bit anxious. What I should have done is get his phone number, but I didn't.
Does anyone know Ed? He's middle-aged, lives in West Medford, has a nice solid commuter ride. Probably now has stitches, too.
Alternatively: what's the best way to seek him out: should I just call Somerville police and see if they can contact him for me?