The CSI effect, if it exists, would be evidence for the validity of social cognitive theory.
Social cognitive theory holds that we expect things to work in the ways that we have seen them work before. The more we see someone act violently without being punished, for example, the more we expect that we can and/or should act violently ourselves without fear of any consequences.
The CSI effect would be evidence that this process actually occurs. As people see forensic scientists and detectives act in certain ways on television shows, they come to expect that the real world should work in the same way. They take the show as a model of reality. Having seen the show play out as it does time and time again, they come to believe that cases in the real world will play out the same way.
In this way, the CSI effect would help to prove the validity of social cognitive theory.