(WASHINGTON) -- The New Mexico teenager who allegedly used an assault rifle to kill his mother, father and younger siblings told police he hoped to shoot up a Walmart after the family rampage and cause "mass destruction."
Police said they are also considering charging the shooter's 12-year-old girlfriend.
According to new information released by police Tuesday, Nehemiah Griego, the 15-year-old son of an Albuquerque pastor, had plans to kill his family, his girlfriend's family, and local Walmart shoppers for weeks before he acted on the impulse on Sunday.
The shooting spree began shortly around 1 a.m. on Sunday, when Griego snuck into his parents' bedroom while his mother, Sara Griego, was asleep. There he raided the closet where the family kept their guns, and immediately used a .22 rifle to kill her, according to the Bernalillo County Sheriff's Department.
Griego then shot three of his younger siblings in the home, including a 9-year-old, 5-year-old, and 2-year-old, and waited for his father to come from his overnight shift working at a nearby rescue mission. When his father, Greg Griego, walked into the home around 5 a.m., unaware of what had taken place, Griego shot him multiple times with the AR-15 rifle, Sheriff Dan Houston said Tuesday.
Greg Griego was a former church pastor at Calvary Church in Albuquerque, and worked as a chaplain at a local jail where he counseled convicts. The family was very involved in the church, according to its website.
Griego then packed up the guns, including two shotguns, as well as ammunition for the rifles, and planned to drive to a Walmart to shoot additional people.
Houston said that Griego called his 12-year-old girlfriend Sunday and ended up spending the entire day with her rather than going to the Walmart. Around 8 p.m. on Sunday, the pair drove to Calvary Church and someone on the church's staff then called 911, Houston said.
"At this time, Nehemiah had been contemplating this for some time. The information that Nehemiah had contemplated going to the local Walmart and participating in a shooting in there is accurate," Houston said. "There is no information at all that he went to church to cause anyone bodily harm there. The suspect also contemplated killing his girlfriend's parents."
The girlfriend's name was not released, but police are investigating whether to press any charges against her, Houston said.
Sheriff's deputies were dispatched to the Griego home around 9:15 p.m. on Sunday and arrived 10 minutes later, where they found the bodies.
Griego quickly confessed to the crime, telling investigators he was "frustrated" with his mother. Deputies said he was "unemotional" and "very stern" during the confession.
Griego reportedly gushed to police about his love for violent video games during the interrogation, Houston said.
Houston said that Griego had occasionally lost touch with his family and then reconnected with them multiple times in his life. He told investigators that his father had taught him how to shoot the weapons and the pair had practiced shooting them together.
Griego has five older siblings who were not living at the home at the time of the shooting and were unharmed.
He is facing murder and child abuse charges and will be tried as an adult, according to police.
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