Nehemiah Griego, 15, is seen in an undated photo provided by the Bernalillo County Sheriff's Deptartment. Griego is charged with killing five family members on Jan. 19, 2013, including his father, mother, and three youngest siblings in Albuquerque, N.M. Authorities in New Mexico say Griego had reloaded his guns after the attacks and planned to go to a Wal-Mart and randomly shoot people. Instead, they say he texted a picture of his dead mother to his 12-year-old girlfriend, then spent much of Saturday with her. The two went to the church where his father had been a pastor, and Griego eventually confessed to killing his parents and three younger siblings. AP Photo/Bernalillo County Sheriff's Deptartment Bernalillo County Sheriff Dan Houston, right, and Lt. Sid Covington answer questions about the shooting deaths of five family members during a news conference at the sheriff's headquarters in Albuquerque, N.M., on Tuesday, Jan. 22, 2013. Authorities have charged Nehemiah Griego, 15, with murder and child abuse counts in connection with the slaying of his family. Bernalillo County District Attorney Kari Brandenburg answers questions during a news conference in Albuquerque, N.M., on Tuesday, Jan. 22, 2013, about the potential legal aspects in the case of a 15-year-old boy who is accused of gunning down his family. Nehemiah Griego remained in custody Tuesday on counts of murder and child abuse resulting in death. Bernalillo County Sheriff Dan Houston prepares for a news conference at the sheriff's headquarters in Albuquerque, N.M., on Tuesday, Jan. 22, 2013, regarding the shooting deaths of five family members over the weekend. ALBUQUERQUE, N.M. (AP) - The New Mexico 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 randomly shoot people, authorities said Tuesday. Instead, 15-year-old Nehemiah Griego texted a picture of his dead mother to his 12-year-old girlfriend, then spent much of Saturday with the girl and her family, authorities 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. He did not give any further explanation. Houston said Griego had planned the shootings for at least a week, but it's unclear if he ever actually went to a Wal-Mart or why he changed his mind about continuing the attack, which occurred the same day thousands of gun advocates gathered peacefully at state capitals around the country to rally against stricter limits on firearms. 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. "We know Nehemiah had been contemplating this for some time," Houston told reporters at a Tuesday news conference. Griego apparently had told others of his plans, but whom and when was still under investigation, Houston said. 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. The case was assigned to public defender Jeff Buckels, who didn't immediately respond to a phone call seeking comment. According to Houston and charging documents, it all began early Saturday at the family's home in a rural area of southwest Albuquerque, when Nehemiah Griego - angry and annoyed with his mother - acted on what he described to investigators as homicidal and suicidal thoughts. Houston said the teen shot his mother while she slept at about 1 a.m. with a .22 caliber rifle that the parents kept in a closet. He said he killed his siblings after they woke up and became upset, then grabbed a semi-automatic rifle his parents owned and waited in the downstairs bathroom to ambush his father as he returned from work at a rescue mission around 5 a.m. Griego told authorities he then reloaded the two guns and put them in the family van. Houston said he didn't know if Griego actually went to a Wal-Mart, but officers found the two rifles, as well as at least a dozen rounds for the .22 and a handful of rounds for the .223 caliber assault rifle in the van. Griego spent most of Saturday with his girlfriend and her family, Houston said. At about 8 p.m., Griego went to Calvary church and told church members that his family was dead. Church officials called 911 and took Griego to his home, where he was arrested that night. Griego initially told responding officers he had come home Saturday morning after spending time at a friend's house to discover his family dead, court documents say. The teen later confessed to shooting his mother because he "had anger issues" and was annoyed with her, the records say. The teen had no history of mental illness, and drugs and alcohol didn't appear to be a factor, Houston said. He did note, however, that the teen liked violent video games, including "Modern Warfare" and "Grand Theft Auto." Houston did not say whether he believed the games were a factor. Greg Griego was a gang member-turned pastor who had once served at Calvary, one of Albuquerque's largest Christian churches. He had an extensive arrest record from his gang days, but was best known throughout the law enforcement community for his work as a voluntary chaplain. Calvary Pastor Skip Heitzig said in a statement Tuesday that news of the deaths has stunned the church community. "We are doing what we can as a church body to minister to the remaining family members," he said. Only the Lord Jesus Christ can heal this type of pain and heartache. The boy's uncle, Eric Griego, said in an emailed statement Tuesday that "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. A records check by the Children, Youth and Families Department indicated no problems with the family and that Nehemiah Griego had never been in trouble with the law. "This is beyond any human reasoning or understanding," Houston said. It's horrific. What other words do you use? This is certainly the first time that I have been into a crime scene with this much destruction at one home. In addition to the two rifles, there were two 12-gauge pistol-grip shotguns in the home, Houston said. Griego's father had taught him to use guns, and they shot together on a regular basis, Houston said. The house had a security-style sign outside saying: "Protected by Smith & Wesson Security Services." Eric Griego said in the statement that the family was concerned that the tragedy would be politicized as the nation debates gun rights. He called on the media "to not use Nehemiah as a pawn for ratings or to score political points."