Actually, I think it was more than that. He was an enforcement officer for a corrupt and degenerate system that tramples the truth and serves to perpetuate injustice over the very populace that pays its bills. When a system is based on lies, and discourages truth-telling, this is the result that should be expected. You've heard the saying, "the truth will out"? The truth in this matter finally came out and it was more than this former officer's mind could bear.
When you lay down with dogs, you're bound to get up with fleas.
He went into the sewer and couldn’t handle the smell. His manifesto is about racism, perceived slights, and corruption.
If you’re going to be a whistleblower, writing a disjointed, rambling, racist screed and killing innocent people is not the way to go about it.