He’s a mystery man at the trial of three police officers accused of killing an unarmed bridegroom in a 50-shot barrage — variously referred to as the “SUV guy” and the “man in black.”

A parade of both police and civilian witnesses have described him as a cool customer with a cold stare and — as the shooters insist they believed — possibly packing a loaded gun.

His name, lawyers say, is Fabio Coicou. But beyond that, little is known about the key player in the slaying of Sean Bell hours before his wedding.

The witnesses have testified that Mr. Coicou and Bell menaced each other outside a Queens strip club, the scene of Bell’s bachelor party, on November 25, 2006. The brief, closing-time standoff outside Kalua Cabaret has become central to the undercover detectives’ explanation for why they eventually felt compelled to open fire at the car carrying Bell and two friends who were seriously injured.

“The SUV guy was calm, cool, and collect, right?” the defense attorney, Anthony Ricco, asked during a cross-examination of Detective Hispolito Sanchez, who was posing as a strip club patron that night.

“Yes, he was.”

“The SUV guy gave a straight street stare (at Bell), like ‘Go ahead,’ right?”

“Yes sir.”

“And you’re thinking, ‘This is not good. Somebody is going to get shot,’ right?”

“Yes sir.”

Mr. Coicou disappeared into the night before the real trouble started.

Detectives Michael Oliver and Gescard Isnora face manslaughter charges in the case, which sparked community outrage and raised questions about police use of deadly force. A third detective, Marc Cooper, is charged with reckless endangerment.

Prosecutors have portrayed detectives as trigger-happy and poorly supervised. The defense contends the officers, after witnessing Bell and his friends trade insults with Mr. Coicou, became convinced they were going to Bell’s car to get a gun.

Mr. Coicou apparently was living in Georgia when he resurfaced about a year ago to testify before a grand jury investigating the shooting. When the trial started last month, he was on the prosecution witness list — a sign he was ready to tell his story publicly for the first time.

Still, no Mr. Coicou.

Prosecutors have so far declined to say when — or even if — he will be called to testify at the closely watched trial.

The officers claim that the shooting began only after Detective Isnora identified himself as a police officer and that Bell, who was behind the wheel, nearly ran him over and smashed into one of the police cars. A supervising lieutenant has testified that amid the confusion he believed his men were the ones under fire.

No weapon was found in the car. Though they didn’t know his identity at the time, police first made note of Mr. Coicou in a report prepared immediately after the shooting.

The report describes how, while investigating allegations of prostitution at the club, undercover officers noticed “an unidentified (man) wearing all black clothing.” The man was “standing next to a black SUV with shiny rims, parked directly in front of Kalua Cabaret,” and at one point “placed his right hand inside his jacket pocket, simulating that he had a weapon,” the report said.

Prosecutors say that though strangers, Mr. Coicou taunted Bell because he was drunkenly trying to re-enter the club. One of the Bell’s guests testified that he heard “the guy in black” say to Bell, “You can’t be going in there. I’ve got money in there” — a possible reference to his dancer girlfriend.

Another friend described how Mr. Coicou, hand tucked in pocket, stared down Bell. “Of course I thought he had a gun,” the friend said.

Detective Sanchez claimed to have overheard Bell say, “Let’s f—him up,” and his friend twice blurt out, “Yo, go get my gun.” As Bell and his friends walked away — unaware that police were trailing them — Mr. Coicou got in his sport utility vehicle and slowly drove away. Moments later, Detective Sanchez heard the fatal gunfire ring out.