Police activity on the T-Third

@caltraindiaries Twitstress (?) Laura O. sends the following report, which she estimates took place a little after 1 p.m.:

Was walking back from lunch and saw a flurry of cop cars. Roughly 6 cars, two motorcycles and the weird four wheel drive white car zoomed down 4th, past Caltrain and surrounded a T car that was idle at the station.

Literally they surrounded it — it was crazy. Passengers streamed off, and we hurried over to take a look. Looks like two guys got in a fight; one was arrested, the other just walked away. All in all I’d guess that there were 15 + cops.

Also, the T was then sent back to Dogpatch; wasn’t allowed to continue on its normal route.

Anyone know what is or was going on? If the guys were just fighting, why was one allowed to “just walk away”?