Seriously, when are people going to stop being surprised at Fox doing stuff like this?
Fox News is a company whose purpose is to make money. Their way to make money is by selling viewers to advertisers (In this, they are no different from other TV networks or things like newspapers, websites etc). Advertisers like a predictable audience they can characterize as accurately as possible, so they can tailor their products and/or advertisements to cater to said audience.
Fox News is simply trying to ensure that a predictable segment of the population reliably tune in to their station. Since people like hearing other people say things they agree with, one way to do this is by telling that section of the population exactly what they want to hear. And that is what Fox does.
In this case, is an informed, nuanced piece about how video games do or do not influence young gamers' behavior going to appeal to Fox's target audience? No, it is not. Therefore, it's a simple piece about how some violent person played violent video-games, ergo violent video-games turn sweet little kids into serial killers. The people in Fox's target audience who see this will find themselves nodding along with the piece, ensuring they will tune in again next week, same time, same channel.
You could argue (justifiably, IMHO) about whether this model has undesirable social effects, and about news networks' responsibility etc, but this simply doesn't show up in Fox's equation. All they know is that by doing things this way, they can predict who's going to watch, and that is valuable to advertisers. There's no malice in that, it's just business (in their mind, of course)