Courtesy of the Griego Family / Reuters

An undated family photo of Nehemiah Griego, the 15-year-old accused of killing his parents and three siblings. Surviving relatives say he may have suffered a mental breakdown.

Relatives of a New Mexico teen accused of killing his parents and three siblings say he's not a "monster" but a "misguided" boy who may have suffered a mental breakdown.

Police have portrayed Nehemiah Griego, 15, as an "unemotional" video-game fanatic who plotted a killing spree for more than a week because he was mad at his mother and emailed a photo of the slain woman to his 12-year-old girlfriend.

A statement released by an uncle, former state lawmaker Eric Griego, paints a far different picture of a "bright, curious and incredibly talented young man," describing him as a doting older brother who played the guitar and drums, ministered to other youths and hoped to one day join the military.

"We have not been able to comprehend what led to this incredibly sad situation. However, we are deeply concerned about the portrayal in some media of Nehemiah as some kind of a monster," the statement said.

"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."

The statement said that Nehemiah Griego was not a loner and only wore his dad's fatigues because of his interest in serving his country. It cautioned against anyone using the tragedy to make a point about gun control.

"He is a troubled young man who made a terrible decision that will haunt him and his family forever," it said. "Five lives have been senselessly and needlessly ended. Ruining one more without trying to get to the bottom of what really happened and more importantly -- why -- would be equally tragic."

Bernalillo County

Nehemiah Griego, 15, in a booking photo after he was arrested for killing his parents and three siblings.

Bernalillo County authorities said Griego had not been diagnosed with any mental illness and was apparently not on drugs or alcohol when the family was slaughtered Saturday.

Using his father's .22 rifle and a AR-15 semiautomatic rifle, he allegedly shot his sleeping mother, killed his 9-year-old brother and then fatally shot two sisters, 5 and 2. Police say he lay in wait at least four hours for his father, Greg, a reformed gang member and chaplain, and then shot him dead.

According to a timeline provided by police, Griego sent his girlfriend a photo of his mother and later spent most of the day with her before going to church and telling officials there his family was dead.

At one point, he considered killing the girlfriend's parents, as well as shooting up a Walmart and dying in a firefight with cops, police said.

The 12-year-old girl has not been charged with a crime, but the investigation is continuing, sheriff's Deputy Aaron Williamson said Wednesday.

Prosecutors said they plan to try Griego in adult court, though he could face less jail time if convicted because of his age.

Griego had five older siblings who did not live at home and escaped harm.

A 15-year-old New Mexico boy accused of fatally shooting his parents and three of his siblings told his girlfriend they had died in a car crash, according to a probable cause document released Monday to KOB News 4.

Police said the boy, Nehemiah Griego, later admitted during questioning that he shot his mother, brother and two sisters – who were 9 and younger – then waited to shoot his father, a popular Albuquerque chaplain who was not home at the time, according to the court document.

Nehemiah agreed to speak with police without an adult or lawyer present, according to the court document. Police have not confirmed whether the teen, who was booked in juvenile jail, has been assigned a public defender.

Nehemiah was charged Sunday morning with five counts of murder and three counts of child abuse leading to death. Under New Mexico state law, 15-year-olds charged with first-degree murder are tried in adult criminal court. 

What Nehemiah allegedly told police is laid out in the probable cause statement for his arrest that was filed in Bernalillo County Children’s Court Division on Sunday. 

Police were called to the Griego residence in a rural Albuquerque neighborhood on Saturday after receiving a call from a parishioner at Cavalry Church, a local Christian parish where Nehemiah’s father, Greg Griego, had once served as a pastor.

Nehemiah had been at the church and had told his girlfriend that his family had been killed in a car accident. He said that girlfriend's grandmother started asking questions and that he was later called to his pastor's office. 

Church officials, suspicious of the story, called police. Nehemiah initially told police that he had returned home from a friend’s house at 5:30 a.m. on Saturday to find the door to his house locked, according to the document. He told police that he found his father’s "carcass" on the ground floor. 

After finding his mother and brother’s body on his parent’s bed, he then took a set of car keys from his mother’s purse and drove the family van to the church, the document said. 

Arriving at the home, police found five bodies – later identified as those of Greg Griego, 51, Sarah Griego, 40, and three of their 10 children Zephania, 9, Jael, 5, and Angelina, 2. The other children were not home, according to the Albuquerque Journal.

'Horrific' scene after teen allegedly shoots parents, siblings

Griego then changed his story, according to the document, after police asked him why he had driven to the church with two rifles in the van, and why he had not called 911. He said that he did not call 911 because he panicked.

Nehemiah told them that he had been having suicidal and homicidal thoughts. He said he shot his mother with a .22 rifle around midnight as she slept. He said his 9-year-old brother woke up after the gunfire and that he told him he had just shot their mother.

"Nehemiah stated his brother did not believe him so Nehemiah picked up his mother's head to show his brother her bloody face," the statement said. "Nehemiah stated his brother became upset so he shot his brother in the head with the same rifle he used to shoot his mother." 

He then went into the bedroom his two younger sisters share and found them crying. He told police that he shot both of them in the head. Then he said that he went downstairs and waited for his father to return. His father returned at 5 a.m. that morning.

Nehemiah told police he shot his father multiple times with an AR-15 semi-automatic rifle with a scope, according to the document, then said he reloaded the weapons with the intention of driving to an area where he could shoot more people.

He told police that he wanted to die exchanging fire with law enforcement.

Nehemiah told police that he had taken both of the guns from his parents’ closet, and that he had taken a photo of his dead mother and sent it to his girlfriend.

Whether Nehemiah's statement to police can be presented at trial is unclear. Although police say that he was read his Miranda rights, state law demands that prosecutors must prove that the confession was offered only after a "knowing, intelligent and voluntary waiver of the child's constitutional rights was obtained."

The court takes into account the time of day and treatment of the child at the time of questioning, the child's mental and physical condition and whether the child had an attorney, friends or relatives present.

Police and neighbors in Albuquerque were still trying to make sense of what had happened on Monday.

“I’ve never seen anything quite like this,” Bernalillo County Sheriff Dan Houston said at a news conference on Sunday, the Albuquerque Journal reported.

Greg and Sarah Griego were remembered by friends and neighbors as a caring pastor and housewife.

“Chaplain Griego was a dedicated professional that passionately served his fellow man and the firefighters of this community,” said a statement released by the Albuquerque Fire Department. “His calming spirit and gentle nature will be greatly missed. Our thoughts and prayers go out to Greg’s extended family.”

Neighbor Peter Gomez told the Albuquerque Journal that he did not know Nehemiah Griego well but that the accused teen “wore nothing but camouflage stuff.”

Few other details about the alleged shooter were clear two days after the killing of his family members. On Monday, a spokesman for the Children, Youth, and Families Department in New Mexico said that Griego has “no history with the juvenile justice system,” according to the AP.

“Our family is grieving this terrible tragedy,” relatives of the Griego family said in a statement. “We appreciate the prayers and support we have received and request that the media honor our family’s privacy during this difficult time.”

Griego is expected to make his first appearance in court on Tuesday, according to the AP.

NBC staff writer Isolde Raftery contributed to this report.