Update: Suspect arrested.
Transit Police are looking for a man they say got on the Red Line at Ashmont Thursday morning, then took off his pants and underwear and proceeded to "commit a lewd act," which police do not specify but which you can probably figure out.
"This was done in full view of other passengers present," since the Red Line does not have courtesy curtains, Transit Police say.
Police add he got off the train at Savin Hill - after getting dressed again.
If either end of the guy looks familiar, contact detectives at 617-222-1050 or send an anonymous text tip to 873873.