The boys were playing an M rated video game.

It's been years since Dr. Mike Brooks traded in his video game manuals for psychology books.

"I played a lot of video games in my day, and it's not just teens who play violent video games and become more aggressive," he said. "It's probably a subgroup."

The subgroup that Brooks is referring to may include the thirteen-year-old shooter from Marble Falls.

The boy's grandmother said he, the victim and another boy were playing "God of War" when the violence on the screen crossed into real life.

"If there's a lot of trash talking, it's a highly competitive friend, there's pride on the line, friends watching or if you've got a kid who's engaging in aggressive behavior and you add the element of violent video games, that could be the tipping point," Brooks said.

Those elements may have provoked the Marble Falls boy to release his frustration through the barrel of a gun.

Video game designer Ryan Mattson said it's the adult's responsibility to keep the child from reaching that point.

The shooter's grandmother is also his guardian, and said she wasn't present when the violence exploded.

"Monitor what they're playing. If you disagree with something, you as a parent should step in and not allow them to play that anymore," Mattson said.

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	Vide games The 13-year-old shooter was said to have been playing violent video games which could have influenced his behavior.

Brooks said it was a bad idea that the boys played the M rated game in the first place.

"You can weed out some of the games they shouldn't play on the front end. Then the ones that are borderline. The parents should see for themselves, talk to their teen about it, create a dialogue," he said.

Police said the victim is in critical condition at an Austin hospital.

The other teen is in police custody and charged with aggravated assault with a deadly weapon.

Experts said of course not all video games are bad.

Some educational games and even the popular Super Mario Bros. are great for stimulating learning.

But any game can become addictive which is why experts suggest letting kids play no more than one-to-two hours a day.