I’d say it’s a case of plausible deniability.
They didn’t want it to come to trial, because it would be a race-baiting clown circus, with the media jumping through hoops.
Also, possibly, because he was fired earlier from the LAPD not for lying about his fellow cops, but because he spoke out when he was supposed to shut up and go along with it. That would by no means excuse his going around shooting people, including innocent victims who had nothing to do with his firing. But it might explain why the LAPD wanted him dead.
Also, he was going around shooting LEOs all over the place, which is not a permissable activity.
This appears to have been rough justice. On the other hand, even if his charges against the LAPD were true—which is in question—I think he had earned the death penalty for many deliberate murders, and more in the future if he was given the chance. And California has no death penalty for murder.
I don’t like to see cops taking the law into their own hands—but that’s what happens when the justice system breaks down.
It's what happens when apologists issue apologias, rather than demanding government officials act according to law.
That's all very well and good, but we have this thing called a Constitution and a Bill of Rights and hundreds of years of Anglo-American law that says the government can't kill people without due process except under extreme circumstances that were not met here. And the cops don't get to veto that.