Update 2:15 p.m. Saturday: A 21-year-old man who was set upon by two other Muni passengers on Thursday night says the incident began with a dispute over playing music that another rider objected to.
Dexter Lotz said in an interview with San Francisco's ABC7 that as he played music -- it's not clear over what kind of device -- another passenger on the N-Judah light-rail vehicle approached him.
"He said, 'Are you going to get off?' " Lotz told ABC7. "I said, 'Do you have a problem with the music?' He didn't respond. Then I said, 'Are you going to do something about it?' And he attacked me."
Lotz gave a slightly different version of events in an interview with NBC Bay Area.
In yet a third interview -- with independent journalist Anna Sterling, who tweeted video of the Thursday evening incident she had obtained from a witness -- Lotz said that San Francisco police ordered him to the ground and handcuffed him when they encountered him after the incident.
Sterling wrote that when Lotz asked why he was in handcuffs and not the man who had put him in a headlock and attempted to throw him from the Muni vehicle, police told him that reports claimed that Lotz was the aggressor.
Muni rules -- like those on virtually every California transit system -- prohibit playing sound equipment without earphones. Lotz told ABC7 Thursday night's episode wasn't the first time a Muni passenger has wanted him to turn his music down.
"If someone would have asked me to turn it down, I would have done that," Lotz said.
Original post (last updated 5:35 p.m. Friday): San Francisco police are investigating a Thursday night incident captured on cellphone video in which two adult passengers on the Muni Metro appear to assault a younger passenger and then attempt to throw him from the vehicle.
Police said Friday they had located all three men involved in the incident and none sought to press charges. The department said its investigation is ongoing.
Two short videos of the episode, which occurred about 8:45 p.m. Thursday on an N-Judah light-rail vehicle near 34th Avenue and Judah Street in the city's Outer Sunset neighborhood, were tweeted late Thursday.
One of the videos depicts an adult white male who has another person in a headlock on one of the vehicle's seats. Other passengers approach, exclaiming, "He's a kid!" and "Over music?"
A second video shows the first adult and a second, also apparently white, trying repeatedly to force a younger male off the vehicle through an open side door. The younger man, who appears to be a person of color, struggles to stay on the car and screams "Stop!" several times.
The videos were posted by Anna Sterling, an independent journalist and part-time producer for KQED's Forum program.
She said on Twitter that she had obtained the video from a witness who got off the Muni car at the same stop as the young man to offer aid. "He is OK," Sterling reported early Friday via tweet. "He was shaken up after the incident for sure though. We are following up this story and will share soon."
It isn't apparent from the videos what led to the incident. Police said they planned to review Muni surveillance footage, "which may show what occurred prior to the encounter seen in the cellphone videos."
Muni said on Twitter that the N-Judah operator was aware of the incident as it was occurring and notified police. The agency said it had given the SFPD surveillance video from the car.
The Police Department said in a statement that about 8:45 p.m. Thursday, it "received several calls regarding an assault that occurred on a Muni light rail vehicle."
"Officers arrived on scene and made contact with two adult male subjects," the statement said. "During our investigation, both subjects admitted to being involved in a mutual physical altercation, but neither party chose to press charges."
Officer Grace Gatpandan, a department spokeswoman, said later Friday that police had also located and interviewed the apparent victim, who declined to press charges.
"We have an open and active investigation into what happened," Gatpandan said, including "looking at the circumstances" that led to the incident. She added that if police find probable cause a crime was committed, those involved could still face arrest.
Supervisor Katy Tang, who represents the neighborhood where the incident occurred, called the video "very disturbing."
"Violence should never be the answer to resolving issues," she said. "I hope that riders will seek assistance from Muni operators if there are ever any issues on Muni because they are more well-equipped to handle these problems and call for further back-up if needed."
The SFPD asked anyone with information about the incident to call the department's anonymous tip line at (415) 575-4444.
This story was updated Friday to include Friday afternoon comment from the San Francisco Police Department and Supervisor Katy Tang.
This story was updated Saturday to include details from interviews given by Dexter Lotz, the man fellow riders tried to throw off an N-Judah train car.