Not that it matters but do you think Baxter was guilty? (SPOILERS)

Personally, I'd think Baxter was trying to make Johnson THINK he would be understanding him, as he realized that all Johnson was acting upon by trying to destroy his imaginative/projected likeness basically was nothing but a frustrated, desperate desire to communicate and find understanding and insights about himself. Baxter found out that Johnson would let him off the hook of this absolutely senseless violence if he'd give him any answer at all, and tell him he's not alone, so that's what Baxter did, he gave Johnson what he needed, what he had been looking for.

There MIGHT be the possibility that Baxter really believed into what he told Johnson thereby about human nature, either by interpreting Johnson's demons as aggression and violence in general, or as a very specific sexual desire. In case IF Baxter really believed what he said, there MIGHT be the possibility he really felt the same way as Johnson, in general or specifically. And in case IF he felt the same way, there MIGHT be the possibility he acted upon it, either in those specific cases mentioned in the film, or in others. In short, a bit too many IFs and MIGHTs dependent upon each other for me.

However, Baxter failed to give Johnson ALL Johnson needed. He didn't give him the cure Johnson was looking for so desperately, and thereby he authored his own death sentence, for several reasons. Johnson at that point had come to be in such a mentally regressed infant state that Baxter's uttered inability to help him shatters Johnson's just now growing trust and hope in Baxter as a substitute, omnipotently helping parent (by which Baxter actually remains but a faceless projection screen just like before), so Johnson acts out his recurring frustration as aggression and violence again. By losing this potential status of a helping parent, Baxter in Johnson's mind is given back his only alternatively possible role, that of Johnson's personal mirror image that he seeks to destroy in order to destroy his own demons. A third, more or less rationalized level is that of Johnson killing a man that has seen his inner soul and that could now give him away at any given time. Johnson by far prefers to be a factual, known murderer (who is actually "proud" and speaking of his deed because of whom it is that he has slain), instead of being suspected a potential child molester. The act of willfully killing Baxter is furthermore being experienced as positive by Johnson as thereby he finds an outlet to put all his frustration and desperation into, so Baxter also acts as a substitute authority representing values responsible for Johnson's frustration, which is why this act of killing Baxter feels like coming "home" at last even though Johnson's inner demons do not perish.

And it's not only because of the aforementioned that Baxter is not but a peripheral character but also very likely to be innocent, apart from the fact that the only scene where a potential perpetrator is seen, he is nothing but a tiny, unidentifiable pixel on the screen. Several hints are scattered across the film indicating that Johnson has not only been fantasizing about the acts Baxter is being accused of, but that he could be the actually guilty party, such as some of his actions and parts of his dialogue showing much involvement with the ongoing of the investigations that partly can even be interpreted as hampering these very investigations and aggressive behaviour concerning parts of the investigations, flashbacks of himself committing the crime, or the factual fear the girl exhibits concerning him as he finds her and while they are in the ambulance, while she does not seem to feel fear concerning the rest of the police units or that male nurse in the ambulance right beside her.

Therefore, there are three potential parties guilty of the crimes leading to Johnson killing Baxter. Either it really was Baxter, or it was nobody we knew, or it was Johnson himself. Baxter, as previously noted, exhibits the least amount of hints indicating he could have done it, including his trying to make Johnson feel understood and his probably drunken, disoriented state when he is found in town. There is not much dirt/filth or any blood on his clothings that Johnson so vividly and obsessively describes later as being all over him. The only noticeable character trait that we get to see about Baxter beside the fact he's married, two children, moderately well-living, is that he is or for a long time has been basically every schoolbully's victim, a fact that probably makes him able to realize over the course of their dialogues what specifically Johnson is looking for. However, it also makes him easy prey of Johnson's bullying that gets out of control completely by the moment as Johnson finally gets an answer about himself that he has been looking for from Baxter, yet no cure.

Johnson's past of experiencing horrible crimes, even though eating at him, is nothing but an excuse he's telling himself and others. As Cartwright tells Johnson, millions of police officers deal with it and worse every day, however they don't run around killing people because of it. Cartwright has not constantly been turning his back on Johnson and continues to do so because he would be denying obvious facts. His reason for not facing Johnson is his intention of making it easier for Johnson to talk without an authoritative figure's inquisitive gaze upon him that would obviously silence him.

Johnson's years of police work are furthermore an excuse as Johnson obviously has never been able to part with his job, by asking about a transfer to another department instead of homicides and/or rapes, or by quitting police alltogether and getting a different kind of job. Most likely, Johnson became a member of the police simply to hunt down and to one way or the other destroy his likeness in manyfold incarnations in order to destroy his inner demons.

However, considering the vagueness of the whole film and that it is not focussing on the matter of who did it but on Johnson's state of mind instead, it might be save to say that most likely the moderate answer inbetween, in the middle should be the right one. We don't see the actual perpetrator in the film, neither Baxter nor Johnson did it. The only thing that matters is that Johnson would have LIKED to do it and has been fantasizing of doing it, while these inner demons of his have not perished by the end of the events the film chronicles.

It's not a film about who did it, it's a film about what more wrong things ensue afterwards, about certain mental patterns of most outrageous forms of moral panics being based on trying to extinguish personal inner demons in one's projected likeness, and about what forces people to project their demons like that, a projection that makes it completely impossible to find out who or what actually did it. In doing so, its dialogues and some of its pictures portray in most harsh, staggering, disturbing terms the unspoken, unnamed, and unthinkable which due to being ignored or denied leads to crimes, be it hate crimes such as Johnon's killing of Baxter caused by ignored social patterns enforced by masses upon the individual, or other crimes caused by mental patterns that are getting completely obscured by projection.

How do you know?

Calvin's interpretationm makes at least as much sense as yours.