Six years ago today, rap and film star Tupac Shakur was fatally wounded in a drive-by shooting on a crowded street a block from the Las Vegas Strip.

Despite the public setting and the victim's notoriety, no one has ever been arrested for the killing. Shakur's family, many of his followers and some black entertainers cite the case as evidence of a double standard in the justice system. Had a white celebrity been gunned down in the open, they contend, police would have found those responsible without delay.

Las Vegas police say their investigation stalled not for lack of effort, but because witnesses in Shakur's entourage refused to cooperate.

That, however, is only part of the explanation. A Times review found that police committed a string of costly missteps:

• They discounted an incident, hours before the shooting, in which Shakur took part in the beating of a gang member in a Las Vegas hotel lobby.

• They failed to follow up with a member of Shakur's entourage who witnessed the shooting and told police he might be able to identify one or more of the assailants. The witness was killed several weeks later in an unrelated shooting.

• They did not pursue a lead about a sighting of a rented white Cadillac similar to the car from which the fatal shots were fired at Shakur and in which the assailants escaped.

Las Vegas homicide Sgt. Kevin Manning, who oversaw the investigation, defended his department's work. He said detectives fielded thousands of phone tips, interviewed hundreds of witnesses and chased numerous leads during a year when the homicide unit was besieged with a record 168 murders.

"Tupac got the same treatment as any other homicide here," said Manning. "But you know what? We can't do it alone. We rely on cooperative citizens to step forward and help us solve crimes. And in Tupac's case, we got no cooperation whatsoever."

The Times reported Friday that court documents as well as interviews with investigators and gang members, including witnesses to the crime, indicate that Shakur was attacked by the Southside Crips, a Compton gang, to avenge the earlier beating of one of their members. The Times also reported that the man who had been beaten fired the fatal shots.

The following account of how the Las Vegas police investigation went aground is based on the same sources and on interviews with Nevada police, six Los Angeles-area investigators involved in the probe and three independent gang experts.

Gang killings are extremely difficult to solve because there is usually little evidence and few witnesses are willing to talk. Shakur's associates were particularly unlikely to volunteer information. Like the rapper himself, many had criminal records and a deep-seated hostility toward police. To some extent, the feeling was mutual: Shakur first gained notoriety with lyrics depicting violence against police.

There was a deeper problem: Las Vegas police were slow to grasp that the roots of the killing lay in a feud between rival gangs in Compton, and were slow to act once they did realize it. To identify those responsible, police would have to take their investigation to Compton and develop informants within the gangs.

The Vegas cops were ill-suited to do that. They had little experience with gang investigations or gang culture. The Compton Police Department did have entree to the gang underworld. Its investigators had known many gang members since they were babies. They took their first mug shots. They testified at their trials. They visited them in jail. In return, they often got valuable information.

But Las Vegas police worried that the Compton investigators were too close to the gangs and their rap-industry patrons and might leak information. The Vegas detectives kept their distance from the gang squad, and their investigation quickly hit a dead end.

"How is a cop from Vegas supposed to go out to Compton and get a powerful street gang to cooperate in a murder probe?" asked Jared Lewis, a Modesto police detective who is director of Know Gangs, a group that presents seminars on gang homicides for police agencies nationwide.

"Gang homicide investigations are very complex," he said. "This was no easy case to solve, by any stretch of the imagination. I can understand why it ended up the way it has."

Sept. 7, 1996

On the evening of Sept. 7, 1996, Shakur and his record company chief, Marion "Suge" Knight, attended the Mike Tyson -Bruce Seldon heavyweight boxing match at the MGM Grand Hotel. Also in Las Vegas for the fight were scores of gang members from Los Angeles.