1) District Attorneys in 1971 were even more incompetent than they are today. Harry secured evidence from the killer without a warrant, so none of the evidence was admissible against the killer. However, the killer had already beaten Harry and shot at another cop--couldn't he have been charged with those crimes? No wonder Harry went fascist!
2) It's okay to be a bigot as long as you're bigoted against ALL other races and aren't just picking on one or two of them.
3) Police inspectors are allowed to carry .44 magnums as their service weapons. Apparently they weren't too worried about negligently putting a hole through their target and pretty much any bystander within 100 yards of it.
4) Next time some psycho commandeers your school bus and takes you and the other kids hostage, and he asks you to sing, just sing dammit.
5) If you got stabbed in the early '70s, bright red paint will come out of the wound. My theory is that blood back then flowed bright red due to all the LSD.
6) Paying off the killer at the very beginning would have saved three more lives plus about ten times more money in damages caused by Dirty Harry.