Stakeout on Dope Street (1958)

Three teenagers find a briefcase with a beat-up old can in it. They throw away the can and pawn the suitcase. When they read in the papers that the can was full of uncut heroin and belonged to a drug dealer who killed two narcotics agents in a shootout, they go back to look for the can, find it, and decide to go into the heroin-selling business. However, the drug dealer's gang also wants the heroin, finds out the boys have it, and sets out to hunt them down and get back their dope.