The Salt Lake County SWAT team defused a four-hour standoff in the township of White City early Saturday, persuading a suicidal man who had reportedly fired shots into the air outside his home to surrender.

But as officers left the scene, they forgot a potentially dangerous part of their operation in front of a neighbor's house: an M4 assault rifle.

The oversight horrified the Salt Lake County Sheriff's Office and unnerved residents in the township near Sandy, who wondered what could have happened had the weapon been found by children or anyone other than a resident who quickly took the gun inside and called police.

Salt Lake County Sheriff's Deputy Levi Hughes said the gun was left by a veteran member of the SWAT team who forgot the weapon in the grass while packing up gear after the standoff ended.

A homeowner found the rifle in the front yard of a house on the 10200 South block of Zinnia Way a few hours later and notified authorities. An officer on patrol stopped by the home and recognized the rifle as a weapon belonging to the SWAT team, Hughes said.

"It's a terrible mistake," Hughes said. "For this to happen one time is unacceptable. The public expects more out of us than this. We're going to take every step possible so that this never happens again."

Hughes said the SWAT team responding to Saturday's standoff consisted of employees from the Salt Lake County Sheriff's Office, Taylorsville Police Department and Unified Fire Authority. He declined to name which agency the officer who forgot the gun worked for, but said the officer is a "veteran," and as a member of the SWAT team, is generally regarded as among the most highly skilled law-enforcement members in the area.

The officer will face disciplinary action, but the offense likely won't result in termination, Hughes said.

He said SWAT team officers have a process called "resetting" after responding to each incident, in which officers carefully pack away each piece of equipment used during a situation. It's unclear how the officer got distracted and missed packing the rifle.

The SWAT team responded to the White City incident at about 9:30 p.m. Friday, when a woman told police her 35-year-old husband had just fired a gun into the air. Several other residents had also called to report four to five shots coming from the home.

The man's wife escaped from the house and told police her husband had combined several prescription drugs he was taking with alcohol, and was talking about suicide.

Police responded to the home and asked the man to come out, but he refused. About 40 officers were stationed outside the home as officers negotiated with the man, who finally surrendered at about 2:15 a.m. Saturday.

He was taken to a psychiatric unit at University Hospital and will be arrested on suspicion of domestic violence after his release, Hughes said.

"To the public, some might look at it like 'I'm glad nobody got hurt,'?" Hughes said. "To us, it's as devastating as it gets."

mrogers@sltrib.com

lwhitehurst@sltrib.com