Two New York policemen have pleaded not guilty to manslaughter and assault charges over the shooting of an unarmed man on the day he was to be married.
A third officer has pleaded not guilty to assault charges.
Sean Bell, a 23-year-old black man, was killed last November when police fired nearly 50 shots at his car as he left a club after celebrating his stag night.
The shooting prompted outrage in the city and triggered accusations of racism against the police.
Two other police officers present at the time of the shooting have not been indicted on any charges.
Intent to harm
The BBC's Guto Harri in New York says the charges are among the most serious which can be levelled against serving police officers.
Detectives Michael Oliver and Gescard Isnora have been charged with manslaughter in the first and second degrees, implying both intent to harm and recklessness.
Mr Isnora was the first to shoot and is accused of firing a total of 11 bullets. Mr Oliver is accused of firing 31 of the nearly 50 bullets aimed at Mr Bell and his two companions.
The detectives opened fire in the belief, they have said, that the men were going to Mr Bell's car to get a gun.
Sean Bell was shot dead by police officers on 25 November
The policemen have said that Mr Bell's car hit an unmarked police vehicle and the officers thought someone in his car was reaching for a gun. No weapon was found.
The police officers were conducting an undercover investigation at the nightclub in the Queens district of New York, which was being investigated for prostitution, underage drinking and weapons complaints.
The three officers entered their plea in front of a packed courtroom that included Mr Bell's fiancée, his mother and two friends who were wounded during the shooting.
Mr Oliver and Mr Isnora were granted bail of $250,000 (£129,000) and Detective Marc Cooper, pleading not guilty to assault, was released without bail.
The shooting prompted outrage in New York and street protests from activists demanding murder charges for all five police officers involved.
Our correspondent says the killing was widely seen as a disturbing sign of racism within the New York Police Department.
Three of the officers involved that night were black, two were white. Two of Mr Bell's friends, both black, were injured in the shooting.
Mr Oliver and Mr Isnora face a possible 25 years in jail. Mr Cooper, who fired four shots, could spend up to a year in jail.