This is on the tip of my tongue, but it was a book that I read somewhere between 2015 and 2020, in English, either as a paperback or an electronic book (I don't think I listened to it as an audiobook), part of a series with at least three books (that's as many as I remember reading). I don't remember if the main character was actually a detective, or just needed to occasionally find out more information, but what's sticking with me is that he occasionally kills the undead (the bad ones), and one of his informants is a zombie who resides in a heavily fortified movie theatre. One of the reasons for the zombie picking the location was that it was already built to be air conditioned (I think with an indication that the dead body of the zombie tended to decay and/or just smell when not kept cold) and that the zombie in question was a bit of a cinephile. They might have also been really into music, because I remember that the main character "pays" for information with rare collectibles, and I think one of them was a record. Although, in retrospect, it might have been a film reel, and part of me also wants to say that cigars and whiskey (said zombie could still smell and taste them) were part of the bribe.
The zombie has an extensive computer network, which is how they ferret out information, and the theatre's heavily fortified with security doors, booby traps, and weapon turrets. In one of the books, the main character realizes that his informant has been compromised, and tries to contact them to let them know, but only gets a dead connection. When they arrive, they find that the informant has survived, although the bad guys nearly got through their defenses, and they're rightly paranoid that the main character was the source of the attack.
I want to say that the zombie was described as being very pale-skinned, and maybe dressed in loud colors.
That's everything I can think of at the moment, will add more later if it comes to me.