I have no dog in the fight of Chris Dorner or the LAPD. I don't live in LA. Never met Dorner.
From all of the evidence I've seen and read, Dorner is insane. The LAPD knew that he was dangerous and fired him and put him in the files so that if other PDs hired him he was flagged. Dorner realized he couldn't get a job as a cop so he went insane and started killing cops and their families. This all started when Dorner applied to be a cop and started behaving irrationally at the job. So they terminated him before it could escalate into him becoming a workplace killer.
You see...the LAPD were smart. They recognized that Dorner was insane and did everything that they could to get him off of the streets and not walking around armed. They saw a paranoid nutcase and knew that it would not be wise to give him a gun and badge. His ex-wife said the exact same thing a few years ago before any of this murder spree happened. Was she in on the conspiracy with the LAPD as well to discredit Dorner? Or maybe...did she divorce a lunatic and then warn others not to date him? Which one seems more logical?
And he proved them right by becoming a mass murderer who targeted police. He wanted to murder hundreds of people. His manifesto is him directly wishing that he can kill as many police and their family members as possible. Does this sound like someone you'd want walking around with a badge and gun? Not in my neighborhood thank you.