NEW YORK CITY: Police are scouring Brooklyn for 19-year-old Corey Arthur, a former student of Jonathan Levin who they believe may know something about the killing. In an answering machine message left last Friday, when police believe Levin was slain, the boy told Levin, "I need to see you. It's important." Arthur is known to have visited Levin at his apartment several times previously, sources say. Police note, however, that the killer probably did not act alone. A fuzzy security video shows one or two individuals standing close by a young black man withdrawing $800 on Levin's ATM card at an Upper West Side Chase Manhattan Bank, police now speculate that anywhere from one to three other assailants were involved in the killing. The video has been sent to the FBI in Washington, D.C. for further analysis.