A Utah teen accused of fatally shooting his mother and three siblings last week was charged Wednesday in their murder, according to reports.

Prosecutors say 16-year-old Colin J. Haynie killed his mother and sister as they were returning home. He then allegedly waited for two more siblings to come home and killed them, too.

He tried to kill his father, as well, but the 50-year-old managed to wrestle a handgun away from Colin despite getting shot in the leg, prosecutors said in court documents.

Haynie is charged with four counts of aggravated murder, one count of attempted aggravated murder, and five counts of discharge of a firearm with serious bodily injury -- all felonies, Salt Lake City’s Fox 13 reported.

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

It’s still unclear what was motivating the teen, Broadhead said. Authorities suspect the teenager used a family handgun, but that is still under investigation. Each family member was shot shortly after entering their Grantsville home, which is about 40 miles west of Salt Lake City, Broadhead said.

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Consuelo Alejandra Haynie, 52, and her 12-year-old daughter, Maylan Haynie, were killed first by multiple rounds. Colin Haynie's 15-year-old sister, Alexis Haynie, also suffered multiple gunshot wounds, and his 14-year-old brother, Matthew Haynie, was killed by a single gunshot wound to the head, prosecutors said.

His father spoke to police shortly after the quadruple slaying but has not talked to the investigators since, the county attorney said.

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.

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A funeral for Consuelo Alejandra Haynie, her 15- and 12-year-old daughters, and her 14-year-old son will be held Friday. The injured husband and father, 50-year-old Colin Haynie, has been released from the hospital.

The family moved to Grantsville in 2010 and 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. It wasn’t immediately clear if has a lawyer who could speak on his behalf.

The Associated Press contributed to this report.