NEW YORK - Since the killing last week of Jam Master Jay, the disc jockey for Run DMC, the Police Department has been using its own experts on the sometimes violent world of rap music to better understand what forces - if any - from that world may have led to the crime.

A team of detectives who study the industry, tracking the artistic clashes and business rivalries that at times escalate to bitter disputes and bloodshed, has been poring over Web sites, attending clubs and reviewing tips from informants to help solve the crime, said Lt. Brian J. Burke, a police spokesman.

The detectives, working closely with investigators from the Queens Homicide Task Force and the 103rd Precinct, have brought 10 years of department experience in the music world to the hunt for the killers of the 37-year-old disc jockey, whose real name was Jason Mizell.

The broad investigation into the killing of Jam Master Jay, who was shot in the head on Wednesday night as he sat on a couch in the lounge of a recording studio in Queens, has not yet uncovered a solid motive, the police said.

Yesterday, investigators were focusing more on a man with a longstanding grudge than on rap-world warfare or some other business dispute.

Hip-hop liaisons

But the detectives who spend their days navigating through the worlds of rap and hip-hop were working through the weekend on the murder investigation as well as on preparing for Jam Master Jay's funeral on Tuesday.

Several investigators from the unit were interviewed but asked that their names not be used because of the nature of their work.

The team of six detectives, drawn from both the department's Gang Intelligence Unit and a little-known group called the Priority Targeting Section, has revisited song lyrics and reviewed industry disputes and rap-related crimes for leads in the murder case, officials said.

When not investigating a specific crime, the detectives serve as police liaisons to the worlds of rap and hip-hop, meeting with artists and promoters, as well as investigating violence, money laundering and other crimes in the music industry, and they talk to detectives who do similar work in places such as California and Florida, several investigators from the unit said.

They also look at the criminal histories of figures in an industry that has often glorified crime and the gangsta life, tracking who gets in trouble with whom, one detective said.

The detectives also closely monitor whose compact disc sales are climbing and whose are not, and listen to song lyrics.

Sorting grudges

Among the difficulties they face is weighing the credibility of various threats, one senior police official said. They must separate the manufactured clashes, which one detective suggested some rappers hype to increase their record sales, from those that could truly result in violence.

The investigator noted a widely reported feud between the rappers Jay Z and Nas. "If you listen to the songs they sing, you would think Jay Z and Nas hate each other, but they hang with each other," the investigator said.

"I've talked to both of them; they have no beef with each other. They know if they act like they're fighting with each other, they can sell more CDs."