(ABC News) -- Relatives of a New Mexico teenager accused of killing his mother, father and younger siblings with an assault rifle, then telling police he hoped to shoot up a Walmart, are described as stunned by his actions and "heartbroken over this senseless tragedy."
Though surviving relatives conceded in an unsigned "family statement" that 15-year-old Nehemiah Griego is a "troubled young man," the statement also described him as an outgoing boy who loved music and hoped one day to serve in the military.
"We know him as a bright, curious and incredibly talented young man. He was a brother, nephew, grandson and cousin," said the statement, obtained by the ABC News affiliate KOAT in Albuquerque from former New Mexico state Sen. Eric Griego, the suspect's uncle.
"We are deeply concerned about the portrayal in some media of Nehemiah as some kind of a monster," said the statement. "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. What we do know is that none of us, even in our wildest nightmare, could have imagined that he could do something like this."
Nehemiah Griego, the 15-year-old son of an Albuquerque pastor, had plans to kill his family, his 12-year-old girlfriend's family and local Walmart shoppers for weeks before he acted on the impulse on Sunday, according to police.
"Nehemiah said after killing five of his family members he reloaded the weapons so that he could drive to a populated area to murder more people," read a police report from the incident released Tuesday.
"Nehemiah stated he wanted to shoot people at random and eventually be killed while exchanging gunfire with law enforcement," the report said.
However, after allegedly killing his family members, Griego ended up spending most of his day with his girlfriend rather than going to the Walmart, Bernalillo County Sheriff Dan Houston said Tuesday.
Griego later was arrested and is expected to face adult charges of murder and child abuse resulting in death. He waived his right to arraignment in adult court Tuesday and a judge ordered him held without bond.
The district attorney's office and Griego's public defender now are preparing to face a grand jury, KOAT reported.
"We never had a case like this, as far as I know, in the state of New Mexico," District Attorney Kari Brandenburg said, "so I can't compare this to any other case."
Police also are considering charging Griego's girlfriend, who they have not named publicly.
Griego has five older siblings who were not living at the home at the time of the shooting and were unharmed.
Eric Griego, the uncle who released the family statement, also released family photos late Tuesday, including one of his nephew in a tuxedo at a wedding and another of him playing a drum kit.
Eric Griego is the brother of Greg Griego, a former church pastor at Calvary Church in Albuquerque who also is the father Nehemiah Griego is accused of killing.
"From the time he was a young boy, his father Greg supported his love for music," the family statement said. "Thanks to his interest, practice and natural ability, Nehemiah has become a very accomplished musician. He plays guitar, drums and bass. For years he has played at youth and other church services at Calvary and elsewhere.
"The idea that he was a loner also has been manufactured by the media and those who simply did not know him," the statement said. "He had many friends at Calvary where he spent most of his free time playing basketball or music. Like his father, who was a champion wrestler and coach, Nehemiah also competed in wrestling tournaments throughout the state and country."
The statement noted that several family members were military veterans.
"Pictures of [Nehemiah Griego] being circulated in his dad's old fatigues were part of his interest in someday being a soldier," the family statement noted.
The shooting spree began shortly around 1 a.m. on Sunday, when Griego allegedly sneeked 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's 9-year-old brother was sleeping with his mother at the time and woke up. When Griego told the boy his mother was dead, the youngster didn't believe him, according to a police report.
"So Nehemiah picked up his mother's head to show his brother her bloody face," the report said. "Nehemiah stated his brother became so upset so he shot his brother in the head."
He then went into his sisters' bedroom, police said.
"Nehemiah stated when he entered he noticed that his sisters were crying and he shot them in the head," the police report said.
The girls were 5 and 2 years old.
The teenager 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, Houston said Tuesday.
Besides being a former pastor at Calvary Church, Greg Griego worked as a chaplain at a local jail where he counseled convicts. The family was very involved in the church, according to its website.
The complaint said Nehemiah Griego took a photo of his dead mother and "sent it to his girlfriend."
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 -- but ended up at his girlfriend's house instead, Houston said.
Around 8 p.m. on Sunday, the pair drove to Calvary Church. Griego told people his family had died in a car crash. 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. Houston said she had some knowledge about the deaths during the day Sunday.
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 five bodies.
Nehemiah Griego told investigators he came home around 5 a.m. that morning and found his family dead. He said he then took the guns to protect himself.
But he admitted to the crime when pressed by police, telling investigators he was "frustrated" with his mother. Deputies said he was "unemotional" and "very stern" during the confession.
"The motive was purely that he was frustrated with his mother. He could not articulate to our investigators any farther," Houston said. "In the time our investigators spent with him, it was a very casual [statement], he was just frustrated with how things were, and would not even articulate any further details of that frustration."
"It's horrific," Houston added.
A police report from the incident shows that Griego admitted to having "homicidal and suicidal thoughts" in the time leading up to the incident.
Griego reportedly gushed to police about his love for violent video games during the interrogation, Houston said. He told police he loved to play Modern Warfare and Grand Theft Auto.
"The suspect was involved heavily in games, violent games, it's what he was into," Houston said. "He was quite excited as he discussed this with our investigators."
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.
The family asked the media not to politicize Nehemiah Griego's death.
"Our family has differing views on gun rights and gun control," the family statement said. "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.
"He is a troubled young man who made a terrible decision that will haunt him and his family forever," the family said.