Jimmy didn't continue to wait for Jack to deal with Slim; he's already got part of the intel, and naturally needs to proceed with investigating the photos and names.
Normally, he should keep interrogating Slim for everything about Hammer — personality, address, habits, residence, phone, etc. But for Jack right now, this informant or gang member clearly played him, and this is his way of getting back at him. There really aren't many chances to speak peacefully with such a gang about town. Getting this much is already quite good, at least better than before.
Jimmy also worked as a police officer, though less than two years, but he knows what kind of mess city police are. So now is not the time to delve into the details. If needed, he can find some other reason to contact Jack.
Driving away, Jimmy looked in the rearview mirror at Jack and Slim still in the small grove. Whatever, Jack probably won't go too far, let's pretend he didn't see it.
