Internal Affairs officers are investigating after an off-duty NYPD cop appears to have randomly opened fire at a passing car Tuesday night in Pelham, N.Y., hitting a passenger six times.

NYPD Commissioner Bill Bratton says alcohol may have been a factor, and one witness says he believes road rage sparked the shooting.

Pelham police say the 27-year-old officer, Brendan Cronin, is believed to have fired his NYPD-issued 9 mm handgun at a passing car near Lincoln Avenue and Sixth Avenue just off the Hutchinson River Parkway at about 11:55 p.m..

The 47-year-old passenger in that car was shot in the torso, arm and hand, police said.

Witness Travis Hood said he was outside his apartment when he saw a driver get cut off by another car.

The driver "was screaming at the top of his voice, climbed out the window -- not even opened the door, he just sat on his window and just 'pow pow pow pow pow,'" said Hood.

"He emptied his clip, and I heard his clip go off," he said. "Emptying his clip, that's not self-defense, that's rage."

Hood said he quickly ran away, frightened by the violence: "I was out of there, I was gone."

After local police responded to the shooting, they found the NYPD officer driving along Lincoln Avenue with his hazard lights on. They followed him to New Rochelle, for about a mile, when he stuck his gun out the window, according to Pelham police.

Police ordered him to toss the gun and his keys out the window, and arrested him.

He is charged with assault. Lawyer information wasn't immediately available.

Janet Gessner, who lives about a block away from where the shots were fired, also said she heard about five shots in rapid succession.

"Boom, boom, boom, boom, boom," she said. "I didn't hear anything else."

Hood, who has not spoken with police about what he saw, said of Cronin: "He should be an example as a cop. I mean, really, everybody gets road rage, but you're a cop."

--Andrew Siff and Michael George contributed to this story