It definitely isn’t (close to) the most important thing to take away from this incident, but I don’t think it needs to go completely ignored either.
There is definitely something about a cop (and it isn’t just this guy, it is a growing trend among the police) having a phone screen, patch, squad car decal (etc.) of a character who is a murderous vigilante, who considers himself judge, jury, and executioner (because the police/legal system doesn’t work), that doesn’t sit right with me.
I realize this was his phone, not uniform or police car, but yes, I still think you shouldn’t have that screen while in uniform.
I admit that it being a phone screen in this case can be seen (and perhaps is) nitpicking, but as a teacher at a Catholic school, I guarantee you that I could get a lot of angry parent emails (and possibly in actual trouble) if had certain comic/tv/movie characters on my phone (while at work), or pictures on my desk.