Hip-hop pioneer Jam Master Jay was gunned down at his recording studio Oct. 30 in New York. He was 37.Police were checking out varying theories about the killing of the rap group member, born Jason Mizell, including whether this was a result of a persona feud or linked to an East Coast-West Coast rappers battle. Many in the rap industry questioned whether Mizell, known as a family man and social activist, would ever be caught in a violent flare-up. He was part of the pioneering hip-hop group Run-DMC, along with Run (Joseph Simmons) and D.M.C. (Darryl McDaniels). Group is credited with being the first rap artists to cross into mainstream popularity and the first hip hop group to have a gold (1984’s “Run-DMC”), platinum (1985’s “King of Rock”), and multiplatinum (1986’s “Raising Hell”) album. Known as the group’s DJ, he spun and scratched records on twin turntables simultaneously, creating a new style and sound that was copied by endless disc jockeys. “If Grandmaster Flash was the first famous DJ, Jay had to be the second,” said Andre Harrell, a Mizell contemporary who now heads Nu America Music. Group’s popularity had waned in recent years but remained venerated due to many milestones, including being the first hip-hop group with a Rolling Stone Magazine cover and the first to have a video played on MTV. Group recently finished touring with Kid Rock and Aerosmith and were scheduled to perform Oct. 31 in half-time festivities at a Washington Wizards basketball home game. “Before the media rushes to attribute this to East Coast-West Coast violence, they should examine Run-DMC’s two decades of contributions and Jam Master Jay’s personal character,” said hip-hop mogul Russell Simmons, whose brother co-founded the group. Bereaved fans outside the crime scene laid flowers, candles, personal notes and an Adidas sneaker — a reference to the group’s hit song “My Adidas.” He is survived by his wife and three children.