Why do copycat crimes or attempts seem to be relatively common?

A man was arrested in Ohio for taking weapons to a movie theater, with what appears to be the intention of shooting people watching The Dark Knight Rises. At least 2 other similar arrests (that I’m aware of), have been made in the past few weeks.

Not that I really understand of these types of crimes in general, but I really don’t understand the appeal of doing exactly what someone else has done. Down to the same movie. Are there studies behind copycat crimes? Is there any explanation for what tempts people to mimic the same scenarios as other violent criminals?