Nehemiah Griego pleaded guilty Friday to killing five family members. He was 15 when the crime occurred in January 2013, according to the Associated Press.

Griego pleaded guilty to two counts of second-degree murder for killing his parents. He also pleaded to three counts of child abuse resulting in death, for killing his three younger siblings. They were named Angelina, Zephaniah and Jael.

Friday's hearing and plea ended two-and-a-half years of a long legal process. He will stand another trial in January, which will determine whether he will be sentenced as a juvenile or as an adult. Based on this decision, his sentence could be probation and detainment in a juvenile facility until age 21. He could also be charged to serve three life sentences, plus 30 years.

Griego shot and killed his parents and three siblings. Authorities say that after this, he reloaded his guns with the intention of opening fire at shoppers in Wal-Mart, according to Inquisitr. He changed his mind, however, and went to see his girlfriend after the murders instead, police say.

"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," a statement from Griego's family members said.

Griego shot and killed his brother Zephaniah, 9, first. Jael, 5, and Angelina, 2, were shot next. He then waited for his father Greg to come home. Greg was working at a homeless shelter when he arrived home and was fatally shot by his 15-year-old son. The rifles Griego used were in the home, unlocked, according to The Albuquerque Journal.