A former South Dakota mayor has been arrested and charged with three counts of murder over a triple slaying in the area that he used to represent.

Jay Ostrem, 64, was arrested following the deaths of three victims on Monday night. He was detained by the Turner County Sheriff’s Office, where he had also reportedly once served as a detective.

The incident was reported at around 10pm on 27 May at a residence in the city of Centerville.

“Jay Ostrem has been arrested and charged with three counts of First Degree Murder, and law enforcement has secured the scene,” said Attorney General Marty Jackley. “There is no further threat to the public.”

Mr Ostrem worked in law enforcement for more than two decades in Wyoming and South Dakota, media reports said. He served as mayor of Centerville about a decade-and-a-half ago, but the exact dates weren’t immediately available.

The names of the three victims, aged 21, 26 and 35, have not yet been released by police pending notification of next of kin. It is understood that two of the men were brothers.

According to the state attorney general’s office, Mr Ostrem is being held on a $1m cash only bond in the Minnehaha County Jail, following the incident.

Authorities did not list a motive for the crime. However, in a complaint filed on Tuesday, obtained by the South Dakota Searchlight, Mr Ostrem justified his actions by claiming it was in retaliation to a sexual assault on his wife.

One of the three men killed was the alleged perpetrator of the sexual assault, the complaint stated. Another was a relative of that man, who called police to report the shooting before being shot himself.

A man had called 911 to report that his brother had been shot by “a guy from across the street,” and that the gunman had returned home.

Police said the man remained on the phone with a dispatcher when a gunshot rang out and then yelled that he was shot. After that, police said, he went silent.

“After some time on the phone with the dispatcher, the male calling party then reported he had been shot,” the affidavit said, reported by Sioux Falls Live. “Shortly after he reported he had been shot, the male stopped communicating with the dispatcher.”

A third man was also found dead in the home, though his relationship with the brothers was not specified.

The affidavit stated that Mr Ostrem’s wife told police that the fatal events came after her disclosure to him that one of the victims had sexually assaulted her at their home on Thursday evening as he slept.

The man lived across the street from the Ostrems.

Per The Searchlight, upon learning of the incident Mr Ostrem “got up and went raging out of the house.” His wife stayed inside until police arrived, which happened shortly after Mr Ostrem was found walking near his home with an “AR-style rifle” and a .380 pistol.

A South Dakota Game, Fish and Parks conservation officer was the first to encounter Mr Ostrem after the shooting, the affidavit said, who noticed “an odor of consumed alcohol”.

He complied with the officer’s commands to stop walking, and he told the officer he had a pistol in his pocket.

The date for Mr Ostrem’s initial appearance on the Turner County charges has yet to be set.