Griego spent most of Saturday with his girlfriend and her family, Houston said. At about 8 p.m., Griego went to Calvary church and told church members that his family was dead. Church officials called 911 and took Griego to his home, where he was arrested that night.
Griego initially told responding officers he had come home Saturday morning after spending time at a friend's house to discover his family dead, court documents say. The teen later confessed to shooting his mother because he "had anger issues" and was annoyed with her, the records say.
The teen had no history of mental illness, and drugs and alcohol didn't appear to be a factor, Houston said. He did note, however, that the teen liked violent video games, including "Modern Warfare" and "Grand Theft Auto." Houston did not say whether he believed the games were a factor.
Greg Griego was a gang member-turned pastor who had once served at Calvary, one of Albuquerque's largest Christian churches. He had an extensive arrest record from his gang days, but was best known throughout the law enforcement community for his work as a voluntary chaplain.
Calvary Pastor Skip Heitzig said in a statement Tuesday that news of the deaths has stunned the church community.
"We are doing what we can as a church body to minister to the remaining family members," he said. "Only the Lord Jesus Christ can heal this type of pain and heartache."
The boy's uncle, Eric Griego, said in an emailed statement Tuesday that "it is clear to those of us who know and love him that something went terribly wrong. Whether it was a mental breakdown or some deeper undiagnosed psychological issue, we can't be sure yet."
A records check by the Children, Youth and Families Department indicated no problems with the family and that Nehemiah Griego had never been in trouble with the law.
Sheriff's Deputy Aaron Williamson confirmed there was no history of any emergency calls to the home in the recent past.
"This is beyond any human reasoning or understanding," Houston said.
"It's horrific. What other words do you use? This is certainly the first time that I have been into a crime scene with this much destruction at one home."
In addition to the two rifles, there were two 12-gauge pistol-grip shotguns in the home, Houston said. Griego's father had taught him to use guns, and they shot together on a regular basis, Houston said.
The house had a security-style sign outside saying: "Protected by Smith & Wesson Security Services."
Eric Griego said in the statement that the family was concerned that the tragedy would be politicized as the nation debates gun rights. He called on the media "to not use Nehemiah as a pawn for ratings or to score political points."