cohort

colleague, coworker, equal, peer, workmate

accomplice, affiliate, ally, collaborator, confederate, half, partner

buddy, chum, confidant, familiar, friend, hearty, intimate, pal

countryman

classmate, housemate, messmate, playfellow, playmate, roommate (also roomie), schoolmate, shipmate, teammate

attendant, escort

hanger-on, leech, parasite

collaborationist, collaborator, informant, informer

evidence, state's evidence

companion, comrade, crony, henchman, partner

conspirator, plotter, traitor

gangster, mobster, racketeer