For marijuana smokers in the right neighborhoods, there is no need to go out for supplies. A dealer-businessman will come right to the door, sit at the dining room table and open a box that looks as if it could be used to display herbal tea choices in restaurants. This particular case, however, is used to show varieties of cannabis — weed — and the businessman will annotate the flavor and potency of his offerings. Bought and smoked behind closed doors, the pot in such transactions has almost no risk of attracting attention from law enforcement.

That was not the system used by Joseph Griffin, then 18, one summer night in the East New York section of Brooklyn. He walked a few blocks down Herkimer Street, made a purchase and headed back to smoke it at home.

“The plainclothes officers pulled up, and they asked me where I was going,” Mr. Griffin said. “I said, ‘Home.’ They jumped out. They was patting me down. He went into my pocket and found it. Then they put the handcuffs on.”