Brian would be going to jail. Not for killing his wife, but for the multiple felonies he commits while proving he didn't murder his wife. While the police aren't totally blameless (did anyone see them get a warrant for that bug they placed on Kim?), Brian would be going to jail for a really tremendous, super-long amount of time for lots of things, but these are the highlights:
Resisting arrest and assault against the first two police officers who tried to arrest him.
Stealing a police officer's gun.
Downloading police files illegally (the ONLY thing that Forest Whitaker's character actually calls him on).
Impersonating a police officer.
Escaping police custody with more assault on police officers.
Kidnapping a police officer (holding the gun on the guy in the police car).
Causing many thousands of dollars in property damage during the pileup on the freeway. (Again, the police aren't totally blameless here - they start shooting at the car he's in even though one of their OWN PEOPLE is still in it).
Vehicular assault and possibly manslaughter during said freeway pileup.
Murder. Lots of murder. The guys in the convenience station, the Russian guys - he tracked them down and killed them all. That's murder, folks! Even though they were all bad guys trying to kill him, he still totally murdered them. In the first degree, even!
Illegally entering an airfield and crashing into a plane (these two are maybes, since his daughter was on board, but I'm betting that the FAA doesn't give a flying fuck).
Look, in the first movie, he was killing bad guys in France and he had a buddy who was sort of looking the other way until he turned out to be a dick. Even there, though, they were pretty intent on getting his ass OUT fairly early on. In the second movie, he was killing bad guys in Istanbul, where one assumes that law enforcement was turning a blind eye to more killing of bad guys. Though if you recall, Brian has to go and hide in a U.S. embassy for a minute and he has his CIA friends helping him smooth things over).
In this movie, Brian has support from his CIA friends, yes, but this is *at least* a citywide manhunt for a guy who's going around causing major traffic incidents and slaughtering gangsters. I know that L.A. has a reputation for not having the greatest police force on the planet, but I'm thinking that Brian would have to deal with more than dirty looks from the guys he made look like incompetent asses, and, y'know, ASSAULTED.
Looking back more objectively, I remember being surprised that Brian got out of France with Kim so easily and also surprised that he was able to leave the embassy in Istanbul, so I guess that this complete disregard for laws shouldn't be a surprise with any of these films. However, this time the manhunt was far more public and he assaulted WAY more police officers during it.
I think that my admittedly large amount of suspension of disbelief that I have for these movies may be done. Or, y'know, not, since it's Liam Neeson hunting people down and fucking killing them, LOL.
All of that said, I think I like this one better than the second one, oddly enough. I liked the police cast and it was cool to see his CIA friends being slightly more involved, smile emoticon.