A father killed his four young children and their mother before turning the gun on himself, said authorities in Wichita, Kansas – marking the second incident of familicide in the midwest in two weeks.

The Kansas Bureau of Investigation and Winfield police department said a man identified as 53-year-old Ronald Williams Sr called police at 8.50am on Tuesday to say he had killed his entire family and was about to take his own life.

When officers arrived at the home, they heard a gunshot.

“At that point, they retreated. There was no other indication of any other loss of life, and so standard protocol was to set up a perimeter and start working the incident as a barricade situation,” said Robbie DeLong, the Winfield police chief, during a press briefing.

After a Swat team broke through the door at 11am, they found Williams and five other people dead: 44-year-old Kelly George and their four children, named as Carol Williams, 9: Ronald Williams Jr, 7: Sarah Williams, 5, and Kelly Magee-Williams, 3.

DeLong said his department had received reports of Williams exhibiting “aggressive behavior”, including confronting and yelling at people in public over the past several weeks.

Officers had previously responded to the area of the family’s home based on reports of gunfire but had not been able to identify the source.

“We have calls of just aggressive behavior, but not enough really to act on,” DeLong said, before adding that there had been “some erratic behavior” but that he couldn’t “say anything would have indicated that we would be where we are today”.

DeLong also noted that this shooting was one of the hardest things he has ever seen:“In my 20-plus years here, no, I can’t remember anything remotely close to this.”

The KBI said it had not determined a motive and would be contacting neighbors and people who knew Williams. Officers with local and state police were also being connected with mental health resources.

Williams was reportedly a registered sex offender, according to the state sex offender registry seen by NBC News. According to Kansas criminal court records, a judge accepted guilty pleas by Williams in 1999 to two felony counts of attempted indecent liberties with a child and one count of battery involving the same victim, a 15-year-old girl.

This harrowing incident comes just two weeks after a Michigan man fatally shot his wife and six children.

Kristopher Karolkiewicz; his wife, Amanda; and their six children, aged five to 15, all died of gunshot wounds before their bodies were found in their burning home in Grand Haven Township on the shores of Lake Michigan. Investigators said the fire had been intentionally set.

The Michigan mass murder was the 13th in the US this year, according to the nonpartisan Gun Violence Archive. Tuesday’s killings in Kansas raise the total to 15.

At least nine of those fit the definition of what since the 1980s has been known as a family annihilation, a type of crime most commonly committed by an armed male on multiple close family members.