Amadou "Ahmed" Diallo, 22, died after he was hit at least 19 times as he entered his Bronx apartment building. The bullets pierced him in every major organ including his heart, lungs and liver.

"It looks like one guy may have panicked and the rest followed suit," a police official told The New York Times on Friday.

Friends said Mr Diallo emigrated from Guinea-Bissau after fleeing civil strife in Mauritania in 1997. He worked 12 hours a day as a peddler, sending much of his earnings back to his parents.

As he returned home on Thursday, four undercover police officers investigating a recent shooting of a cab driver approached him and identified themselves.

Police sources said Mr Diallo reached into his pocket and the officers, who are all white, thought he was going for a gun.

Mr Diallo died at the scene. A beeper and wallet were all that were found beside his bullet-riddled body.

"The police told me it was a mistake," Mr Diallo's roommate, Momodou Kujabi, told the press.

Civilian shootings

The officers, three of whom have shot civilians in the past, were all police veterans with five years or more on the force. They have been placed on administrative duty.

Police Internal Affairs and the Bronx District Attorney are investigating the shooting.

"I'm hoping they'll come forward and tell us what happened, but at this point it's very hard for me to make a judgment because I have very few facts," said New York Police Commissioner Howard Safir.

State Senator David Paterson said the number of shots fired by police suggested they must have carried on firing at Mr Diallo when he was already on the ground.

'Firing squad'

Al Sharpton is planning a vigil for Mr Diallo

Black activist Al Sharpton, who has planned a vigil at the site of the shooting, said: "Are we talking about policing or are we talking about a firing squad?"

Amnesty International USA said the shooting appeared to conform to a pattern of ''police brutality and unjustifiable force'' which had emerged in the New York Police Department over the last few years.

Relatives described Mr Diallo as a devout Muslim and avid basketball fan, who neither smoked nor drank, and was hoping to go to college.

"We have a very undemocratic society back home, and then we come here. We don't expect to be killed by law enforcement officers," his friend Demba Sanyang told the New York Times.