GRANTSVILLE, Utah (KUTV) -- Since news broke Friday that a woman and three children were shot to death inside their Grantsville, Utah home, police have kept details of the killings largely to themselves.

That changed on Wednesday, when 16-year-old Colin Jeffrey "CJ" Haynie was formally charged with the aggravated murders of his mother and younger siblings, and with the attempted murder of his father.

He will be charged as an adult, per Utah law, and faces four counts of aggravated murder, one count of attempted murder and five counts of felony discharge of a firearm, Tooele County DA Scott Broadhead announced in a press conference Wednesday afternoon. The maximum penalty Haynie could face would be life in prison without the possibility of parole, according to Broadhead.

Broadhead said news of the killings reached police just after 7 p.m. Friday, when a neighbor called 911 to report she'd gone over to the Haynie home on Eastmoor Drive and met CJ Haynie, who told her he'd killed his family.

The neighbor and her husband drove CJ and his injured father, Colin Haynie, 50, to Mountain West Medical Center in Tooele. There, CJ Haynie was arrested.

Broadhead laid out the following timeline of when police believe Haynie's family members were shot:

• 1:00 p.m.: Mother Consuelo Alejandra "Alex" Haynie, 52, arrived home from picking up her 12-year-old daughter Milan. The two are believed to have been shot as they entered the home.
• 2:00 p.m.: 15-year-old Alexis Haynie arrived home from school and was shot and killed.
• 5:17 p.m.: Matthew Haynie, 14, returned home from school and was shot in the head, Broadhead said.
• 6:15 p.m.: Colin Haynie arrived home and was shot in the leg as he entered. A struggle ensued and Colin Haynie was struck in the head multiple times with an unknown object. The father was ultimately able to wrestle the handgun away from his son, Broadhead said. He reportedly told police in an interview that CJ Haynie told him "his mother and siblings were dead and his intention was to kill everyone in the home except himself."
• 7:00 p.m.: The neighborarrived and called 911 to report the killings, then drove Colin and CJ Haynie to Mountain West Medical Center.

An adult son, who has not been publicly named but who Broadhead said is 24 years old, was not home the day the shootings occurred and was not harmed.

"This is something that methodically happened over a five-hour period," Broadhead said, "not a one-moment 'snap.'"

Police believe the five family members were shot with a family handgun. The night of the shooting, Utah Governor Gary Herbert tweeted instructions for Utahns to "secure your firearms!"

With the charges, a community left reeling from the news finally has more information. But, Broadhead acknowledged, even police aren't yet sure of the "why."

"We all have those same questions — 'Why?'" Broadhead said. "We don't know. Hopefully, that will be developed through time."

Those answers may come through forensic investigation of computers and cell phones taken from the home. And, the DA said, there is "a lot still going on with the crime scene."

CJ Haynie is expected to make his first court appearance on Monday.