SALT LAKE CITY >> A Utah teenager shot and killed his mother and sister as they returned from school pickup, then waited for two more siblings to come home and killed them, prosecutors said today.

Colin “CJ” Haynie, 16, tried to kill his father as well, but the older man managed to wrestle a handgun away despite a gunshot wound to the leg, prosecutors said in court documents.

The boy from the small town of Grantsville west of Salt Lake City was charged with 10 felonies, including aggravated murder and discharge of a firearm.

“This is something that methodically happened over a five-hour period. … This wasn’t a one-moment snap,” Tooele County Attorney Scott Broadhead said at a news conference. “We all have the same question: Why?”

The Associated Press does not typically name juveniles accused of crimes, but the seriousness of the case and Haynie’s age meant he was charged as an adult under Utah law. No attorney was immediately listed for Haynie.

Investigators still don’t know why the teenager killed his mother, sisters and brother, Broadhead said. The boy acknowledged the slayings the night they happened, but hasn’t talked with investigators since, he said.

Authorities suspect the teenager used a family handgun, but that was still under investigation. Each family member was shot shortly after entering the home, Broadhead said.

Consuelo Alejandra Haynie and her 12-year-old daughter , Milan, were killed first by multiple rounds. Then 15-year-old Alexis was shot as she returned home about an hour later. The suspect’s 14-year-old brother, Matthew, was killed by a single gunshot wound to the head when he came home in the early evening, prosecutors said.

The father, 50-year-old Colin L. Haynie, who was the last to come home, said his son told him that he had planned to kill everyone in the family except himself, prosecutors said.

The father spoke to police shortly after the quadruple slaying but has not talked to the investigators since, the county attorney said. He has been released from a hospital.

Colin “CJ” Haynie was charged with four counts of aggravated murder, one count of attempt aggravated murder and five counts of felony discharge of a firearm.

Aggravated murder typically carries the possibility of the death penalty, but prosecutors cannot seek it for minors. The possible prison sentence for a single aggravated murder conviction is 25 years to life.

A funeral for the victims will be held Friday. Alexis Haynie was the goalie on her junior varsity soccer team and loved art and piano, according to an obituary posted today by the Didericksen Memorial funeral home .

Matthew Haynie was an 8th grader who liked soccer, wrestling and anything to do with “Star Wars.” Milan Haynie was a 7th grader who dreamed of being an engineer and enjoyed soccer, volleyball, super heroes and doing art with her sister. They were all born in Utah.

The mother was born and raised in Chihuahua, Mexico, and loved to prepare meals, garden and take care of her fruit trees, the obituary said.

The family moved to Grantsville in 2010. They also have a fifth child, according to an obituary for Alejandra Haynie and the children.

The teenager is scheduled to make his initial court appearance Monday.