ALBUQUERQUE, N.M. -- The teenager accused of gunning down five family members over the weekend ambushed his father as he returned home from an overnight shift at a rescue mission, then reloaded his rifles and planned to go to a Wal-Mart and shoot people randomly, authorities said Tuesday.

Instead, Nehemiah Griego, 15, texted a picture of his dead mother to his 12-year-old girlfriend, then spent much of Saturday with the girl and her family, police said. That evening, the teen went to the church where his father had been a pastor and Griego eventually confessed to killing his parents and three younger siblings.

"The motive, as articulated by the suspect, was purely that he was frustrated with his mother," Bernalillo County Sheriff Dan Houston said.

Houston said Griego had planned the shootings for at least a week. It's unclear whether he ever actually went to a Wal-Mart or why he changed his mind about continuing the attack. Griego told detectives he also contemplated killing his girlfriend's parents, Houston said.

The sheriff said he didn't know if Griego's contact with his girlfriend avoided further bloodshed. But he said she apparently knew what had happened, and officials are investigating whether she should be charged with failing to report the crime.

The teen waived his right to arraignment in adult court Tuesday on charges of murder and child abuse resulting in death, and a judge ordered him held without bond. -- AP

Deadly crash on Sunrise Highway … Blakeman raise … What's up on LI Credit: Newsday

Wake for NYPD officer ... Deadly crash on Sunrise Highway ... Congestion pricing ... Women's History Month: Jockey Madison Olver

Deadly crash on Sunrise Highway … Blakeman raise … What's up on LI Credit: Newsday

Wake for NYPD officer ... Deadly crash on Sunrise Highway ... Congestion pricing ... Women's History Month: Jockey Madison Olver

Latest videos

Newsday LogoSUBSCRIBEUnlimited Digital AccessOnly 25¢for 5 months
ACT NOWSALE ENDS SOON | CANCEL ANYTIME