NEW YORK -- Investigators believe two mysterious men -- one of whom may have had a gun -- could hold the key to learning why police unleashed a 50-bullet barrage that killed a groom leaving his bachelor party at a strip club hours before his wedding.

One man was last seen dressed in black, standing in front of a sport utility vehicle with silver rims and exchanging glares and insults with the groom, Sean Bell. Another man was last seen wearing a beige jacket and running away from Bell's car as five officers fired.

Law enforcement officials provided partial descriptions Wednesday of the two missing witnesses and details about their possible roles based on accounts from undercover officers and at least one civilian.

The shooting has ignited outrage in New York, and civil rights activists Jesse Jackson and Al Sharpton visited the scene of the shooting Wednesday to console the victims' relatives.

Union officials have suggested that the fourth man could have fled with a gun -- a scenario investigators haven't ruled out.

According to an undercover officer, the other witness -- the man in black -- argued with Bell and his companions as they exited a Queen strip club where Bell was having a bachelor party. The officer was part of a vice team investigating complaints about prostitution and drug dealing at the club.

The man, while in front of a black SUV parked outside the club, reached into his pocket as if he had a weapon as Bell challenged him to a fight and one of Bell's companions, Joseph Guzman, said, "Yo, get my gun. Get my gun," according to the officials, citing the undercover detective's account. The officials spoke to The Associated Press on condition of anonymity because the investigation has not been completed.

The officials said the exchange prompted a second undercover detective to follow Bell and three other men as they walked away toward their car, apparently suspecting the men meant to arm themselves and attack the man in black.

The first undercover officer said he lost sight of the group -- including the fourth man he described as wearing a beige jacket -- as they rounded a corner with the second undercover trailing them on foot. Moments later, the second undercover started shooting at the car when Bell, while trying to drive away, bumped him and smashed into an unmarked police van.

Through his lawyer, the detective has insisted that he clearly identified himself as a police officer as he tried to stop them. He also claims he spotted Guzman, then sitting in the passenger seat, make a sudden move for his waistband before he and four other officers fired.

The third victim, Trent Benefield, told police in a brief interview at the hospital that there was never a fourth person. He also claimed Bell became spooked and tried to take off because he didn't know the undercover was a police officer.

But the shooting detective insists that the group he followed numbered four, and that at some point he saw the fourth man run away from the car and disappear into the night.

"There was a fourth person involved -- no doubt," his attorney, Philip Karasyk, said Wednesday.

Another witness seems to back the account: She has told police she looked out the window of her nearby home after hearing gunfire and spotted someone running away from the direction of the shooting scene. She too described a man wearing a beige jacket, the officials said.

On Tuesday, a team of officers searched for fresh evidence near the shooting scene underneath an airport monorail, based on a tip that a man had ditched a weapon there, the law enforcement officials said.

Meanwhile, a law enforcement official close to the case said prosecutors are waiting to examine 911 calls, police radio communications and ballistic reports, which could determine the origin of the deadly shots. Despite a clamor for answers about what happened, the official said it is a complex investigation that requires thoroughness.

All five officers were placed on paid administrative leave while the Queens District Attorney's officer pursues possible criminal charges.

Guzman, 31, shot at least 11 times, and Benefield, 23, hit three times, have remained hospitalized.

The community outrage over the shooting was evident Wednesday in signs taped up on a brick wall of an auto body shop near the shuttered strip club. "Death to Police Brutality and Murder," said one hand-printed sign. "Off the Pigs Who Shoot Our Kids," said another.

A flower wreath on an easel showed a photo of the 23-year-old Bell, his fiance and one of their young daughters, with the words: "Love Yourself, Stop the Violence."

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Associated Press Writer Pat Milton contributed to this report.