New Mexico authorities announced on Tuesday that a 15-year-old boy who killed his family with several weapons including an AR-15 military-style assault rifle enjoyed playing "violent" video games and had planned to go to a local Walmart to shoot random people.

Bernalillo County Sheriff Dan Houston told reporters at a press conference that Nehemiah Griego eventually admitted to the murders of his mother, father and three siblings after initially saying that he had come home to find them dead, according to KRQE.

Houston said that Griego had waited for his mother to fall asleep before gaining access to her unlocked bedroom closet to obtain an AR-15, a .22 rifle and two 12-gauge shotguns. Some of the weapons had been purchased by the father through private sales, the investigation found.

"The teen told authorities after killing his family he reloaded his weapons so that he could 'drive to populated area to murder more people,'" KRQE reported. "He expressed a desire to shoot people at random and eventually be killed while exchanging gunfire with law enforcement."

But the teen instead decided to spend time with his 12-year-old girlfriend before driving to Calvary Church, where his father had once been a pastor. A church security guard eventually called police, who discovered the bodies at the home.

Houston also said that Griego told investigators that he regularly played "violent" video games like "Grand Theft Auto" and "Modern Warfare." The teen said that he had been taught to shoot by his father.

Griego was charged with two counts of murder and three counts of child abuse resulting in death.

Watch this video from NBC News, broadcast Jan. 22, 2013.

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