My prediction: There are 3 killers (All cops)
All of these are the same guy:
-The beginning guy
-The main serial killer (bags over head cases)
-Killer of the jogger
-Killer of the girl whose body washed up
-Denzel
-Rami
Lets get Rami and Denzel out of the way, we see their killings on screen. We know they are killers but not the main guy. Thats 2 of the killers
Peters (suicide guy)- During interrogation, Denzel tells Rami to ask him about Roberts. Obviously Peters didnt kill Roberts because Denzel did. But was he in the area when she was shot? Is the guilt of knowing she got away what caused him to off himself? I believe he was just a registered offender that felt he was about to be framed for the killings and offed himself. He couldnt take it any longer. He was just a pervert.
Leto - Not Leto. The guy in the beginning is clean shaven and does not have a limp. Also, Leto would not have been in the area to abduct the jogger. Leto was with the teen victim after her death since he was the repair man. Went to the scene of the dead teenager, left milk and beer cans there. Shaved her legs and whatever else. Knew about the mileage marker because it was announced over the radio. He was a crime obsessed pervert for sure, but not the killer.
Rami - No way Rami risks going out with Leto in the end and risks being killed if he's the killer. His obsession is starting to tear at his family. He is saved by Denzel.
Sgt Rogers - The beginning guy is never seen or heard from again, or is he? They try to tie him to the current killings as Sparma but with a shaved face and no limp, its obviously not Leto. Could this also be the guy who kidnapped/killed the jogger? Same tags from the beginning chase are seen at the precinct when Denzel first pulls up (Mercedes) . I think its stated he just received a promotion (bought a new whip?), and he also didnt report Leto's stolen car. Was he setting Leto up to be the fall guy? It would explain the possible high mileage of the muscle car at the beginning and the old car he abducted the jogger in.
Heres why none of it matters in the end. The movie is about obsession, crooked police and guilt. There are always more killers. The killer is never caught because in the end, its not about the killers. The obsession with becoming an "Angel" can turn anyone into a monster. Crooked cops are all over, even when presented as the "good guys". Denzel lost everything in the span of 5 years chasing a killer, not for the girls' sake, but for his own piece of mind about his killing of Roberts. This movie tells us that all three killers are police officers, but frames the "innocent" guys as the only weirdos.
Rami - killed Leto
Denzel - killed Roberts
Rogers - serial killer
Other officers/Mortician = complicit in the cover up of Denzel's manslaughter
Denzel becomes Rami's angel.
There is room for a sequel if another body turns up. After all, the killer hasnt been caught. Hopefully they dont go in that direction though. And Denzel doesnt do sequels (except Equalizer)