Extremely long law question: if Tom did something (not illegal) in the past that led to Alan commiting a crime at present, how is Tom legally responsible?

This question is not necessarily a law question. It can be a plot question too, since I want to check for holes in this story idea.

OK, so we have this scenario: it’s the US, 1950. Tom is a criminologist with an unseen sick mind. He love to study about criminals’ mind via observing (and experimenting on) real people. Alan is a criminal. 34 years ago, for some reason (I won’t say what it is) Alan’s father held a grudge against Alan (who at this time was still a baby). Tom came and agreed with the father to set a plan to send Alan to another family. Tom got Alan from Alan’s father, but he sent Alan to a “strange” infertile couple: the wife loved to have a child whereas the husband hated children. As Alan grew up, the father increasingly abused him, while the mother couldn’t do anything to protect him. One day, Alan did something terrible and illegal in an attempt at self-defense (as a result of his father’s mistreatment). Horrified, Alan fled his home and the US altogether. 34 years later, Alan came back to America with a new identity and was now a hitman who didn’t even enter any police suspects list (due to the interaction with criminals and his own childhood trauma). Tom again drew another plan for his experiment: he used a fake name, came and paid Alan to “kill somebody”, then made sure Alan got noticed by the police using various methods and assistance while Alan committed his crime (Tom also made sure during that time his identity remained unnoticed, he was not very well-known among the publish). It only took the police some time to eventually catch Alan.
You can see from the beginning that Tom deliberately led Alan into committing criminal offenses. But none of Tom’s doings seem to be illegal. So how is he legally responsible for the crime Alan directly committed? Can he get away with it, given that Alan never knew who Tom really was and Tom had never let his true identity revealed during Alan’s killing process?

Side question: are there any holes in this idea?