There was a well known case several years ago, I can’t remember the names - the killer took FOUR YEARS to go back and kill the doctor’s wife and son. No one realized who did it because of the time that passed, he blamed him for a failed procedure.
Then after another seven or so years passed, he went back and killed the doctor and someone else. He drove over several states to do this. The second time they figured out who it was.
Colombo and Hercule Poirot would have figured it out at the first murder.
There was a story a few decades ago about a young man who committed suicide on the mound of the USC (Southern Cal) baseball diamond. He left a note. It was remembered that the man was a former top prospect who was signed by the Trojans and promoted as “the next Tom Seaver” until he blew out his arm and it was never right after this. The guy was discarded and he apparently blamed the university for ruining his pending superstar career. He simply couldn’t move on with life. Sometimes, it does take years before this all spills over to a violent act.