A suspect who allegedly attacked a fellow BART passenger with a chain, unprovoked, on board a train in Oakland Tuesday evening has been arrested, but not yet publicly identified.

The circumstances of the arrest are not clear — BART had put out a call to the public to help identify and find the man, as seen below — but KRON4 reports that CHP officers made the arrest on Thursday evening. The man is suspected of attacking another man around 6 p.m. on Tuesday on a Daly City-bound train as it approached Lake Merritt Station, causing injury. The suspect then fled the train.

As the Chronicle reports Friday, via BART spokeswoman Alicia Trost, the suspect was placed on a psychiatric hold so therefore has not been formally booked by BART Police. The suspect's name has not been released as a result.

BART officials also revealed more details of the surveillance video they have of the entire incident. The suspect reportedly boarded the train at Coliseum Station in Oakland on Tuesday, and began to "casually" speak to a female passenger on the train. As BART tells the Chronicle, "The victim then boarded the train at Fruitvale and began talking to both the male and female. The suspect then punched the male in the face and the two got into a fight." It was then that the chain came out, and the victim was struck by it.

As one BART rider on the street says to KRON4, "Who beats somebody with a chain?"

The incident came on just the second day of BART's new Ambassador program, in which unarmed Ambassadors are supposed to be roaming trains and keeping them clean and safe. But it's unclear whether this particular train would have even been part of their rounds, which have been described as only being between 12th Street in Oakland and Civic Center in SF.

Related: BART Police Seek Suspect Who Attacked Rider With Chain