The victims killed in the shooting were identified as a 52-year-old mother, Consuelo Alejandra Haynie, and three of her children: Alexis, 15; Maylan, 14; and Mathew, 14, said the Grantsville City Police Department on Monday in a press release.
Her father, Colin Haynie, 50, was injured in the shooting and has since been treated and released from a hospital, police said. He asked for privacy for his family.
Police officers responded to a call for shots fired inside a home in Grantsville around 7 pm. Friday and found the bodies, the statement said.
The nameless sniper and his father left when the police arrived, police sergeant. Rhonda Fields said. The authorities later found out that someone had taken them to a hospital.
Officers arrested the boy in the hospital, where he surrendered peacefully. He faces four counts of aggravated murder, one count of attempted murder and several counts of criminally unloading a firearm.
While police said the boy was related to the family, authorities refused to specify his age, how he is related or to disclose his name until formal charges are registered.
Since the boy was not cooperating, detectives tried to put together a timeline for the shooting, Fields said.
“The biggest question everyone has is & # 39; why & # 39; and while we cannot respond directly to that, we hope to be able to gather some information … to avoid something like this or to offer support to those in need, "Campos said.
The small town of Grantsville, with 11,000 inhabitants, is about 55 kilometers west of Salt Lake City. Fields said the murders were the city's first homicides in two decades.
Hundreds of community members participated in a candlelight vigil for the victims on Monday night, where a letter from Colin Haynie was read aloud, FOX13 Salt Lake City reported.
"The depths of the sadness we feel are accompanied only by the overwhelming outpouring of love that we feel from Grantsville and the surrounding communities," the letter said, in part.
The Associated Press contributed to this report.