RIVERTON — Police arrested a man who they say shot and killed his 35-year-old brother after a day of arguing.

"It's bizarre to a certain degree that you have a brother shoot his brother then immediately render aid and call 911," said Salt Lake County Sheriff's Lt. Don Hutson said Saturday.

Brothers Steven Shane Knighton, 39, and Shad Michael Knighton, 35, had been together all day Friday moving items between storage sheds, Hutson said.

An argument between the men escalated throughout the day, and by late Friday, early Saturday, Shad Knighton was becoming physically aggressive, walking up and down the street ranting and raving, Hutson said. The man also had been drinking, police said.

Hutson said Shad Knighton broke a window in a neighbor's parked car then threw either a cell phone or a wrench at a passing driver.

"Into the early morning hours, it got to the point where (Steven Knighton) became concerned that his brother was becoming quite violent," Hutson said. "He got a handgun and at some point made a decision that he needed to use lethal force, so he shot and killed his brother."

Police arrived at the scene at 1:53 a.m. — about five minutes after neighbors say they heard gunshots.

Before shots were fired, police say there was a physical altercation between Shad Knighton and Steven Knighton's wife in the entryway of the home at 2458 W. 12875 South. Police said Shad Knighton's roommate also had been at the home and had angered the man.

"We don't know if (Steven Knighton) was in fear for his life, but he made a determination he needed to protect his family," Hutson said.

After firing several shots, Steven Knighton then called police and reported that he had shot his brother, Hutson said. He waited at the house and tried to administer CPR to his brother until officers arrived.

Shad Knighton, who was shot twice in the chest, was declared dead at the scene, Hutson said.

Steven Knighton surrendered without incident and was cooperative with police, Hutson said. He was booked into the Salt Lake Metro Jail for investigation of homicide.

One of the shots missed Shad Knighton and traveled across the street, where it shattered the back window of a neighbor's SUV.

Officers were already en route to the area for the report of an item being thrown at the passing car when they got the call about the shooting, Hutson said.

Police recovered the handgun they believe was used in the shooting, but the home remained an open crime scene Saturday while officers reconstructed the shooting and gathered additional evidence.