Seven years after the killing of rap star Notorious B.I.G., the FBI is investigating allegations that a rogue Los Angeles police officer orchestrated the slaying with rap mogul Marion "Suge" Knight, according to court documents and law enforcement sources.

The FBI is pursuing a 6-year-old theory that then-Officer David A. Mack, acting at Knight's request, arranged for Amir Muhammad, Mack's friend and college roommate, to ambush the rapper outside the Petersen Automotive Museum on Wilshire Boulevard.

Over the years, the LAPD has offered conflicting assessments of the theory, which police at one point took seriously. Documents show that LAPD detectives are now focusing on an alternative theory that centers on a Houston rap entrepreneur.

Mack, Knight and Muhammad, a Southland mortgage broker, have long denied any involvement in the 1997 killing.

"I have stated from the outset that I have nothing whatsoever to do with any of this," Muhammad, who also uses the name Harry Billups, said in a telephone interview Thursday from his attorney's office. "I've done nothing wrong. I don't have anything to hide."

Knight, founder of Death Row Records, also rejected the allegations.

"I don't know David Mack or Amir Muhammad. I've never met them," he said by phone from Mule Creek State Prison, where he is serving time for a probation violation. "The FBI has never contacted me, but I'm glad they are looking into all of this stuff. I hope they solve it."

Notorious B.I.G., whose real name was Christopher Wallace, was gunned down just after midnight March 9, 1997, in front of hundreds of people who had just left a music industry party at the Petersen museum. The Brooklyn rapper was sitting in the passenger seat of a sport utility vehicle at a red light when a lone assassin in a dark Impala pulled up in the neighboring lane and opened fire.

The killing occurred six months after rap star Tupac Shakur was fatally wounded in a drive-by attack in Las Vegas.

No one has ever been charged in either killing.

Early on, detectives speculated that the murders may have stemmed from a rivalry between East Coast and West Coast rappers. Before their deaths, Shakur and Wallace had been feuding, and a rivalry between their record labels, Los Angeles-based Death Row and New York-based Bad Boy Entertainment, had escalated into a series of assaults and shootings.

Each label used gang members for protection, and police investigated the possibility that both killings were committed by members of Compton's Southside Crips gang.

The theory now being investigated by the FBI was first advanced in 1998 by then-LAPD Det. Russell Poole.

According to Poole, Knight had Shakur killed because the rap star was about to leave his label -- and Knight then had Wallace murdered to make it appear that both slayings were the result of a bicoastal rap feud. Poole contends that Knight may have used corrupt police officers to help carry out both murders.

Mack, onetime partner of disgraced former LAPD Officer Rafael Perez, came under suspicion after he was arrested in December 1997 for robbing a bank. He was later convicted and is serving a 14-year prison term.

Mack owned a black Impala similar to the car used in the Wallace slaying, and a witness reported seeing him at the scene. Informants told investigators that Mack may have provided security for Knight. Both men grew up in Compton.

Poole began scrutinizing Muhammad, who was a classmate of Mack's at the University of Oregon, after learning that he had visited Mack in prison in December 1997. Several months earlier, a jailhouse informant had told detectives that Wallace's killer was a Southside Crip who went by a Middle Eastern name, possibly "Amir" or "Ashmir" -- and that his true name might be Abraham or Kenny or Keeky.

A driver's license photo of Muhammad resembles a police sketch of Wallace's killer based on witness descriptions. One witness told police he saw a man who resembled Muhammad outside the Petersen museum the night of the shooting.

Muhammad, in the phone interview, said the account was unfounded. "Anybody who says they saw me there that night or that I had anything to do with this is a liar," he said.