Family, friends and fans continue to mourn the shooting death of Run-D.M.C. disc jockey Jam Master Jay, gathering Monday for a public and private viewing in a Queens funeral parlor.

A throng of police officers held sway outside the home, as their colleagues slowly began to zero in on potential suspects in the October 30 slaying.

The New York Times reports that detectives have focused their inquiry on a Hollis, Queens, man who was involved in a decade-long quarrel with Jay and who allegedly placed a threatening phone call saying he was "coming up" from the South to settle their differences.

Jam Master Jay, whose real name was Jason Mizell, was gunned down in his Jamaica, Queens, studio by an unidentified shooter and an accomplice. Jay had taken a break from laying down tracks and was relaxing in a lounge playing video games on his Xbox. The 37-year-old mixmaster was shot in the head at close range and died instantly. Another man, 25-year-old Urieco Rincon, whom police described in the Times as a "hanger-on," was hit in the leg before the suspects fled.

Police have announced no motive but are probing several theories after interviewing five witnesses who were in the studio at the time of the killing.

One quickly discounted notion: Jay, a devoted father who eschewed violence and rapped about social change, might have been a victim of the purported East Coast-West Coast rivalry supposedly responsible for the murders of rappers Tupac Shakur and Biggie Smalls.

Investigators initially examined the theory that Jay's death might have been the result of a feud centering around one of his prot?g?s, a young hip-hopster named Curtis Jackson, who goes by the stage name 50 Cent.

Jackson, who dissed the high-rolling gangsta-rap lifestyle in his hit 1999 single, "How to Rob," canceled a performance last week after being informed by the police of Mizell's murder.

It was thought that someone may have killed Mizell to get back at 50 Cent, himself the victim of a shooting in 2000. However, police have since shifted their probe to possible financial motives, telling the Times there's no suggestion of a "rap war" going on.

Police also are saying they've established no connection between Jay's death and the slaying in the Bronx on Saturday morning of 31-year-old Kenneth Walker, a rap-music promoter who worked with rapper 50 Cent.

"They are looking to see if he had any recent disputes, any falling out, any strange phone calls," a police official tells the Times, adding that family and friends were mystified why anyone would want to kill Jay.

The official indicated that detectives were planning to interview the unidentified man behind the apparent phone threat on Tuesday in the presence of his attorney.

Another theory posited by police is that Jay's death is somehow linked to a string of violent crimes involving a former crack kingpin.

On Sunday, police released the first description of the shooter--described as a black man, between six- and six-feet-two, weighing approximately 180 to 200 pounds, last seen wearing a black sweatsuit and a black wool cap.

At Jay's wake Monday, he was remembered as a rap pioneer, a turntable wizard and a good man who gave back to the community and even let aspiring hip-hopsters have free reign in his studio.

Meanwhile, fellow artists in the hip-hop community are banding to support Jay's family and others affected by the shooting.

A coalition, including surviving Run-D.M.C. rappers the Reverend Joseph "Run" Simmons and Darryl "D.M.C." McDaniels, along with Jay-Z, Ja Rule, rockers Aerosmith and Kid Rock, R&B star Ashanti, New York City Mayor Michael Bloomberg and Def-Jam cofounder (and Run's brother) Russell Simmons, along with friends and fans, has pledged contributions to a fund in support of the Mizell family and the criminal investigation.

"Many of us lost a dear friend and an inspiration when Jay was killed. The work of the coalition is to see to it that his family gets the assistance it needs as they try to overcome this tragedy," Russell Simmons says in a statement.

Money raised will be earmarked to pay off Mizell's mortgage, cover education costs for his three children and bankroll a $50,000 reward to help catch the killer.

Jay will be laid to rest in a funeral Tuesday.