OAKLAND, Calif. -- Authorities continue to investigate the early Thursday morning officer-involved shooting at the Fruitvale BART station that left an unarmed man dead as questions concerning whether he was restrained during the fatal incident surface.

BART police were called to respond to a fight between two groups of men onboard a train traveling from San Francisco to the East Bay, spokesman Jim Allison said Thursday afternoon during a news conference at BART headquarters in Oakland.

Five officers had gathered at the Fruitvale BART Station platform when the train arrived shortly after 2 a.m., Allison said.

Officers worked to separate the men, who were dispersed inside the train and outside on the platform, according to Allison. BART police did not say how many people were involved in the fight or what spurred the confrontation.

At some point during the effort to bring the men under control, a BART police officer's gun fired one bullet, hitting 22-year-old Oscar Grant, according to Allison.

According to Mike Yost, supervising coroner investigator with the Alameda County coroner's bureau, Grant was pronounced dead at 9:13 a.m. at Highland Hospital.

Allison said the preliminary investigation indicates that Grant was one of the men involved in the altercation that brought police to the station, which was closed until 2:45 a.m., when it was reopened to finish extended New Year's Eve service until 3 a.m.

Three or four people on the platform were put in plastic handcuffs, called "flexi-cuffs," during the effort to bring the scuffle under control, Allison said. While Allison stated Grant was not in handcuffs when he was shot, police said it is unclear if Grant had been cuffed at any point before the shooting occurred.

"A preliminary investigation indicates that Mr. Grant was not restrained when the officer's firearm was discharged," Allison said.

Grant was unarmed and no weapons were recovered at the scene. Authorities said they were still investigating whether the gun was fired on purpose or accidentally.

The BART spokesman’s version of events stands contrary to the claims of some eyewitnesses to the incident interviewed immediately following the incident. Several witnesses who did not know Grant told KTVU they saw him lying on the ground already restrained when the shooting happened.

"He had the zip ties around his ankles and wrists," claimed one witness.

Grant's girlfriend says she talked to him just before he was shot.

"All I know is I heard a loud pop," explained the girlfriend. "I thought it was a gunshot. My last phone call he said 'They’re beating me up for no reason. I gotta go.' And I heard the gunshot. I didn't want to think the worst"

One of Grant's friends who was with him on the train asserted that the officer who shot Grant was heard shouting "Oh my God!" repeatedly immediately after the shooting.

Grant was transported to Highland Hospital and underwent surgery, according to family members.

In the hours that followed, friends and family members gathered at the hospital, offering each other support and worrying about his survival.

Grant's family says his lungs were damaged in the shooting when the bullet went through him and then ricocheted off the ground and re-entered his body. He leaves behind a four-year-old daughter.

KTVU spoke to one young man at the incident who says he got the entire shooting on tape. He says BART police confiscated that tape, but says the video shows the officer pull his gun and fire two or three seconds later.

Officials have not released the name of the officer, who was placed on administrative leave.

BART police patrol bureau Cmdr. Travis Gibson said it is too early to determine the justification for why the officer took his weapon out of the gun's holster.

Gibson said BART police recovered two firearms, one at the Embarcadero Station and the other at the West Oakland Station, earlier in the night. The night was busy on the BART system with New Year's Eve revelers out in full force, Gibson said.

The last fatal officer-involved shooting at a BART station occurred in April 2001, when an officer at the Hayward Station shot a man who later died, according to Allison.

Thursday morning's shooting remains under investigation, Allison said.

"BART continues to investigate the legal aspects of this incident, it is also investigating the internal protocol and procedures," Allison said. "In addition to that, the District Attorney's Office is conducting a separate, independent investigation."

Anyone with information about the shooting is asked to call (877) 679-7000, extension 7040.