A New Year's Day shooting in which a subway police officer fired a deadly shot into the back of an unarmed man has the San Francisco Bay Area demanding answers as authorities appeal for patience.

Oscar Grant, 22, was killed January 1 in a shooting at a subway station in California's Bay Area.

[Image shows that he is a black man and with his daughter.]

Bay Area Rapid Transit spokesman Linton Johnson told CNN affiliate KTVU-TV in Oakland, California, that the officer is presumed innocent and described him as devastated.

Attorney John Burris called the shooting "unconscionable" and said he filed a $25 million claim with BART on Tuesday, alleging wrongful death and violation of civil rights by use of excessive force. BART has 45 days to respond, Burris said.

"It's a clear shooting in the back that should not have taken place," Burris said, characterizing the incident as a case of "overagressiveness by police."

KTVU obtained at least two videos of the incident and its prelude. One video, which KTVU reported came from a train passenger who wished not to be identified, shows three young men against a wall in the crowded Fruitvale station.

Karina Vargas, who also provided a video to KTVU, said the men had been pulled from the train car in front of hers. Video : Watch the events preceding the shooting

Burris said Tuesday that the young men had been celebrating the new year at a popular waterfront tourist spot, The Embarcadero. They were heading home when police pulled them from the train car.

Some of the young men were handcuffed, but not 22-year-old Oscar Grant. The video from the anonymous passenger shows Grant seated on the floor with his back against the wall.

Grant holds up his hands, appearing to plead with police. Burris said Tuesday that Grant was asking police not to use a Taser.

"He said to them, 'Don't Tase me; I have a 4-year-old daughter,' " Burris said.

The interaction on the video is not audible.

Seconds later, police put Grant face-down on the ground. Grant appears to struggle.

One of the officers kneels on Grant as another officer stands up, tugs at his gun, unholsters it and fires a shot into Grant's back.

Burris said the bullet went through Grant's back and then ricocheted off the floor and through his lungs.

Grant, who has a 4-year-old daughter, died seven hours later, KTVU reported.