The chilling acts the 15-year-old boy is accused of defy imagination:

Pumping his mother, brother and two younger sisters with bullets.

Gunning down his dad when he returned home.

Texting a picture of his lifeless mother to his 12-year-old girlfriend.

Plotting to kill strangers outside a supermarket.

But, family members say, Nehemiah Griego is no monster. They can't fathom what could have gone so terribly wrong.

"Whether it was a mental breakdown or some deeper undiagnosed psychological issue, we can't be sure yet," his uncle, former New Mexico state Sen. Eric Griego, said.

"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 family statement 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 a long family history of military service by becoming a soldier.

The family disputed any media characterization that the teen was a loner and said he had many friends and was a wrestler in state tournaments. His father was a champion wrestler and coach.

The family also said they did not want anyone to use the case in the nation's unfolding debate about guns.

"To be clear, our family has differing views on gun rights and gun control. What we do agree on is that those who wish to score political points should not use a confused, misguided, 15-year-old boy to make their case," the family statement said.

"We ask those in the media and those who would use the media to make their political case, to not use Nehemiah as a pawn for ratings or to score political points. He is a troubled young man who made a terrible decision that will haunt him and his family forever."

But authorities painted a far different picture of the teen.

Sheriff: Teen planned shootings for at least a week

Bernalillo County Sheriff Dan Houston 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."

He said that the boy planned the shootings for at least a week. That he told investigators he was frustrated with his mother. That he contemplated killing his girlfriend's parents. That he hoped to continue his killing spree at a Walmart "with mass destruction" and die in a shootout with police.

The teen's demeanor, as he shared all this, was "stern, very unemotional," Houston said.

Now, Griego will stand trial as an adult in the weekend killings, prosecutors announced.