Three NYPD detectives have been cleared of all charges in relation to the shooting death of a groom-to-be on his wedding day.

Fifty shots were fired at the unarmed 23-year-old in 2006 as he sat outside a seedy strip club after his bachelor party.

The case drew allegations from victims' rights advocates of excessive police firepower.

Anger and grief erupted Friday after the verdict was delivered to a packed Queens courtroom that included Sean Bell's fiancee and parents.

Bell's fiancee immediately walked out of the courtroom after the decision, while his mother broke down in tears.

Outside, the scene was more electrified, with many weeping, and some screaming "Murderers! Murderers!" or "KKK!" amid a heavy police presence and a ring of metal barricades set up around the courthouse.

"As the news came from the courthouse it was pandemonium out here," Melissa Grace of the New York Daily News told CTV's Canada AM.

"There must have been a couple of hundred community activists who came out to support Sean Bell and most of them began shouting at the police and people were very emotional, obviously."

Claims of racial discrimination were raised almost immediately.

"Justice was not here today," Leroy Gadsen of the New York National Association for the Advancement of Colored People told reporters outside the courthouse.

"This court, unfortunately, is bankrupt when it comes to justice for people of colour."

Two of the detectives, Michael Oliver, 36, and Gescard Isnora, 29, were on trial on manslaughter charges. Marc Cooper, 40, faced charges of reckless endangerment.

Two other shooters weren't charged.

Oliver and Isnora could have faced up to 25 years in prison, while Cooper could have faced up to one year behind bars.

The trio opted to have Justice Arthur Cooperman decide their fate, rather than a jury.

In the end he ruled the detectives' version of events held up better under scrutiny than that of the victims.

"The people have not proved beyond a reasonable doubt that each defendant was not justified" in firing, he said.

The officers complained they were unfairly portrayed as vicious killers in pretrial publicity, and defence lawyers made the victims out to be dangerous, drunken thugs believed to be armed.

Prosecutors, meanwhile, argued that the victims were minding their own business and were targeted by the officers -- with the rain of gunfire virtually coming out of nowhere.

Grace said there were immediate comparisons to the case of Amadou Diallo in 1999. Also unarmed, the African immigrant was killed when police mistook his wallet for a gun, letting loose a deadly hail of 41 bullets.

The officers in that case were also acquitted -- prompting thousands of people to take to the streets in protest that resulted in hundreds of arrests.

"There are quite a few parallels," Grace said.

"All the victims in both cases were unarmed and the police in both cases were acquitted so people here were remembering that today.

"One of the first things I heard was a woman who was terribly upset and said 'Oh no,' and she was sobbing, 'Amadou Diallo all over again.'"

Bell's family, along with the Rev. Al Sharpton, has held rallies calling for the officers to be held responsible. Two of the officers are black.