Two videos showing a Bay Area Rapid Transit police officer fatally shooting an unarmed, cooperating 22-year-old man have surfaced, thanks to a vigilant teen and an anonymous cameraman.

According to officials, five officers arrived at a subway station around 2 a.m. in response to reports of fighting on a train. Officers handcuffed a group of suspects, and detained the soon-to-be victim, Oscar Grant III.

In both videos, though detained, Grant had clearly not been cuffed.

Mario Pangelina Jr., aunt to Grant's four-year-old daughter, witnessed the events leading up to the shooting.

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"First, an officer grabbed Oscar by the neck and pushed him against the wall," the Oakland Tribune quoted her as saying. "Oscar didn't fight him, but he didn't go down either. He was like, 'What did I do?' Then another officer came up with his Taser and held it right in his face. Oscar said, 'Please don't shoot me, please don't Taser me, I have a daughter,' over and over again, real fast, and he sat down."

Footage captured by camera-phone-wielding Karina Vargas, 19, shows officers had detained several men. Over the proceeding minutes, officers become defensive as groups of yelling youths stand on the periphery and meander past.

At one point, a male shouts, "Yo, f--k the police!"

Vargas several times makes attempts to get closer. When her camera focuses on Grant, he is sitting with his back against a wall, surrounded by others in handcuffs. He holds up his hands, apparently speaking with the officers, when they force him to the ground.

Two officers struggle to turn him over, even as he appears to be strewn across another man's legs, when suddenly one of the men retrieves his gun from its holster.

At this point in Vargas' video, she turns to her immediate left and focuses on an officer wrestling another man to the ground. Then, the shot rings out.

San Francisco's KTVU aired a second video clip from an anonymous witness. In it, Grant is clearly pinned by two officers and completely immobile. Then, without provocation, the officer at Grant's waist draws his weapon and fires.

After the gunshot, as the audio track dissolves into indiscernible shouting and commotion, an enraged onlooker hurls an object at the police. Vargas retreats to her train and peeks the camera at the officers again.

"They just shot him! They just shot him!" she yells. "... I got you, mothaf--kers!"

The victim was fatally wounded when the bullet passed through his back, hit the ground, and ricocheted into his lungs. He died in a hospital several hours later.

Grant's mother and daughter are being represented by civil rights attorney John Burris, who has a history of work on police abuse issues, including the beating of Rodney King. At a Sunday news conference, Burris called the incident "without a doubt, the most unconscionable shooting I have ever seen."

A person close to the investigation told the San Francisco Chronicle that BART officials are looking into the possibility that the officer thought he was firing a Taser and pulled out his gun by mistake.

Last June, a Maryland district court found that an officer who shot a fleeing suspect in the elbow while believing he was firing his Taser was not guilty of violating the suspect's rights against unreasonable search and seizure.

Burris has announced a civil suit against BART for $25 million. He has also recommended that charges of second-degree murder or manslaughter be filed against the officer.

"It's pretty clear from the tape and from witnesses that he wasn't doing anything of a threatening nature to the officer," Burris said at a Jan. 4 press conference.

He added that he's seen footage from three other cameras that captured Grant's slaying.

The Bay Area police are appealing to the public for "calm."

"We are taking this investigation very seriously," said Chief Gary Gee during a Sunday press conference. "As frustrating as it is, I want to stress that we cannot and will not jeopardize this case by discussing details before the investigation is complete."

This video is raw footage from Vargas' cell phone, captured Jan. 1, 2009 in San Francisco.