You might remember that Reynolds is the guy from the beginning of the film (or one of the earliest scenes) that introduces Jack Vincennes and the whole "dirty" Hollywood setting. Jack arrests him for drug abuse. But not only that, Jack also has a deal with Sid where he gives him information about such scandals in the high society so Sid has "good" stories for the Hush Hush Magazine.
So the arrest, but even more so the yellowpress article the enabling of which Jack apparently got $50 for, is what destroyed Reynolds's carreer and made him in turn do another shady job for Sid. And this is ultimately also part of why Jack feels guilty and concerned about Reynolds and why he drives out to the motel to see if he's okay, finding his dead body.
(I don't blame you for missing that, though, it also took me repeated watching to get that connection. It helps that I've seen the movie a thousand times since.)