A hearing began Monday to determine whether a New Mexico teenager who killed his parents and three siblings will be sentenced as an adult.

Nehemiah Griego, 18, pleaded guilty in state children's court in October to two counts of second-degree murder and three counts of child abuse resulting in death. He was 15 when authorities say he fatally shot his family at their home south of Albuquerque in January 2013.

Sheriff's officials said the teen told detectives after the murders that he was angry with his mother and had been having homicidal and suicidal thoughts.

His parents, Greg and Sarah Griego, were well-known throughout the community for more than a decade of ministry work with inmates at the county jail. Greg Griego, an Army veteran, also served as a pastor at one of Albuquerque's largest Christian churches and was a volunteer chaplain with the local fire department.

The weeklong hearing will include testimony from investigators, witnesses and psychology experts.

Griego's attorney has said his sentencing terms could range from probation to three life sentences plus 30 years if he is sentenced as an adult. If he's sentenced as a juvenile, he would theoretically remain in the custody of the state Children, Youth and Families Department until he is 21.

After the killings, authorities alleged that Griego reloaded his parents' two semi-automatic rifles and put them in the family van and planned to gun down Wal-Mart shoppers, though investigators had no information that Griego actually went to a Wal-Mart the day of the shooting.

A security official said that after the shooting, Griego spent much of the day at his church, wandering the campus as dozens of Sunday school teachers were being trained on how to deal with a shooter.

In the weeks after the shooting, family members described the boy as a normal teenager who was close to his family, loved wrestling with his father and brother and played in the church youth band.