First of all, we have to recognize that we can never truly isolate the degree of impact that violence on film (movies and TV) has on violence in real life. People have too much going on that affects them for us to be able to truly determine how much seeing violence on film leads to committing actual acts of violence in real life.
Theoretically, it makes sense that watching violence on film would lead to committing acts of violence. When we see acts of violence on film, it makes us think that violence is a normal thing. This is particularly true when we see depictions of violence where those who commit the violence suffer no consequences for their actions.
But this is not necessarily true in real life. In real life, at least some people can differentiate between what they see on film and what happens in their own lives. They know that what they are seeing on film is simply a story and that they cannot just imitate it in their lives.
Overall, it seems likely that viewing violence on film affects different people to different degrees. This can depend on the individual’s genetic makeup and on the environment in which they live.