What is the psychology of people who idiolize mass shooters, sees them as heroes and replicate their acts?

People require validation of a sort, and when they don't get it, they can take many different paths. Some choose to take the vengeance route to reciprocate their feelings on others. Some just get depressed, and of course there are many other things individuals can do as a response to a lack of validation. Then there's the facet of mental health problems which could, or could not be mitigated.