"You know who lives here?" Cloudy asks Popeye, as they're staked out at a fancy doorman building in Manhattan. When Cloudy tells him it's Joel Weinstock, Popeye's interest is peaked. He says:
"He was the bank on that shipment outta Mexico three years ago." In that moment, we learn one of the two things most important about this Weinstock character: he's a known drug financier, and the fact that Sal is meeting with him is enough to keep Popeye hot on the case.
Later, when we get a chance to see what our cops don't, Weinstock counsels hot-tempered Boca to chill out and take his time doing this half-million dollar heroin deal. He's been around the block, and, he tells Sal, no one's ever regretted taking a moment to be careful.
Sal, however, is new to a deal of this magnitude, and he's afraid of losing Charnier's connection. He won't listen to this elder statesman, and Sal ends up dead, while Weinstock's own case is dismissed for "lack of proper evidence."