There are four different couriers in the district but you only need to interrogate two of them to get the gears running. Like before, you can kill them or recruit them. For this walkthrough, we'll go after Willy Jovino first. He is located in back alley parking lot with three other enemies. It will be hard to stealth kill all of them but you can just take out the one lookout who separates from the party then get near enough to lure the informant. Alternatively, you can just snipe him from afar to disable him then take out the other enemies. After interrogating him, he'll reveal the intel about bagmen ferrying the racket's cash.
The next courier we'll target is Gianni Amici. He's just with one lone guard so you can just get near enough to toss a grenade at their car while they're near to incapacitate the informant and kill his comrade. You can also sneak behind and lure the informant for a stealth interrogation. He will reveal the location of Frankie’s blackmail stash in the Imperial Spa.