NATIONAL NEWS (CNN) — A New Mexico teen accused of killing five relatives and wanting to gun down strangers at a Walmart isn't a monster, his family said.
But no one can explain what exactly happened to 15-year-old Nehemiah Griego.
"It is clear to those of us who know and love him that something went terribly wrong," his uncle, former New Mexico state Sen. Eric Griego, said in a statement. "Whether it was a mental breakdown or some deeper undiagnosed psychological issue, we can't be sure yet. What we do know is that none of us, even in our wildest nightmare, could have imagined that he could do something like this."
The statement, sent to CNN affiliate KOAT, describes the boy as a gifted athlete and musician who was active in youth services at church. It said the teen accompanied his father on mission trips to Mexico and wanted to continue long family history of military service by becoming a soldier.
It's a far different depiction of the teen who, authorities say, wanted to inflict even more misery after the deaths of his parents and three siblings.
Griego told investigators he had hoped to continue his killing spree "at a Walmart, with mass destruction," Bernalillo County Sheriff Dan Houston told reporters.
The boy wanted to end his rampage with a shootout with police, culminating in his own dramatic death.
But that's not the way the story ended. Instead, the 15-year-old will stand trial as an adult for the deaths of his parents and three siblings.
The chilling case has left the Albuquerque area bewildered.
The tragedy started early Saturday morning, when Griego carried a .22-caliber rifle to where his mother and 9-year-old brother slept side by side, an arrest affidavit said.
The teen fatally shot his mother, waking his younger brother Zephania in the process.
When Griego told Zephania that their mother was dead, the younger boy did not believe him, the document stated.
"So Nehemiah picked up his mother's head to show his brother her bloody face," the affidavit said. "Nehemiah stated his brother became upset, so he shot his brother in the head with the same rifle used to kill his mother."
After that, police said, "Nehemiah stated he lost his sense of conscience."
The boy went on to kill his sisters, 5-year-old Jael and 2-year-old Angelina, before his father Greg came home from a volunteer graveyard shift at a homeless shelter.
Authorities believe the father, a former pastor at an Albuquerque church and a chaplain to the city's fire department, was the last to be gunned down in the home.
Most of the victims were shot with the .22, but a semiautomatic AR-15 rifle was also used in the killings, sheriff's Lt. Sid Covington said. Authorities said the weapons appear to have been purchased legally.
The Griegos had five other, grown children, none of whom lived at home, Covington said.
After the slayings, Griego "spent the majority of the day with his girlfriend," Houston said.
He even sent his girlfriend a picture of his slain mother, Houston said.
Authorities arrested the teen after he attended his family's church with his girlfriend, and a staff member called deputies.
Griego was scheduled to appear in court Tuesday to face two counts of murder and three counts of child abuse resulting in death, but the hearing was waived, KOAT reported. The affiliate said Griego's case will go to a grand jury within 10 days.
So far, the teen's comments to investigators haven't shed much light on a motive.
Griego said he was "frustrated with his mother," but did not give any further explanation of that to investigators, Houston said.
The sheriff also said Griego was "involved heavily" with violent video games, and that he "was quite excited as he got the opportunity to discuss that with our investigators."
But the deaths of two parents and three children still have no explanation.
"This is beyond any human reasoning or understanding at this time," the sheriff said.
CNN's Leslie Holland contributed to this report.