Other mistake: After the post-bank robbery shootout, a TV reporter is heard describing the shootout as taking place in a "small southland neighborhood." But earlier one of the detectives was heard ordering road blocks at Flower and Figueroa, meaning the gun battle occurred in Downtown Los Angeles. Hardly a small neighborhood.
Other mistake: In the scene where Pacino is talking with Albert outside, when Pacino starts singing, the soundtrack on Albert's dialogue is way off.
Other mistake: In one scene, Vincent asks one of his subordinates how he is after getting shot. The reply is "Banged up, but I'll live," but the subtitle reads "Hang up, I'll live." (02:06:50)
Other mistake: When Hanna is tailing McCauley in the helicopter, he is informed that McCauley is headed east on the 105. When Hanna pulls McCauley over, you can see the highway sign saying that they are on the westbound 105.
Other mistake: Drucker is able to shoot out a tire on the getaway car at a distance of at least 30 yards, probably more. Later in the scene, he fires at Cherrito from a much closer distance and doesn't even graze him. Apparently shotguns have selective range.
Answer: Waingro helped Van Zandt track down Trejo. Waingro then tortured Trejo and threatened his family if he didn't give up McCauley. With his back to the wall, Trejo gave Waingro and Hugh Benny the details of the bank heist, but Waingro killed Trejo's family anyway and beat Trejo almost to death. Benny then gives the tip to the police on Van Zandt's order.
BaconIsMyBFF
I wonder how Trejo was tracked, I don't remember his name being revealed during Waingro's time with the crew, or any other information.
Well, we never see the crew prior to their first heist. Trejo could have given Waingro his name during the planning of that heist.
BaconIsMyBFF
Waingro met this crew only once. How would he know who Trejo is or where he lives? Right before the heist, Trejo is asked to mislead police away from the heist.