Just days after Sean ‘Diddy’ Combs was warned his life is in danger by a former friend comes news he may be marked for death. RadarOnline.com can reveal Diddy’s possible involvement in an unsolved murder could mean he is in grave danger while sitting behind bars on federal sex crime charges. After being denied bail twice, Diddy was remanded to the Metropolitan Detention Center in Brooklyn where he can potentially come in contact with West Coast gangbangers eager to avenge the 1996 murder of rival rapper Tupac Shakur. Criminal Center’s Christopher Zouks, author of The Federal Prison Handbook, s…