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A registered sex offender with a lengthy criminal history allegedly slaughtered the mother of his children and their four young kids inside their Kansas home, weeks after police had encounters with him over what the chief described as "erratic behavior."

Ronald H. Williams Sr., 53, allegedly killed Kelly L. George, 44, and their four children, Carol A. Williams, 9; Ronald H. Williams Jr., 7; Sarah K. Williams, 5; and Kelly M. Magee-Williams, 3, before making a chilling 911 call Tuesday morning, according to authorities.

Williams allegedly told the dispatcher that he had killed his entire family and was preparing to kill himself.

Officers happened to be working a traffic crash roughly two blocks away and raced to the Winfield home almost immediately, Police Chief Robbie DeLong said during a news conference.

As the first officer approached the house, a single gunshot rang out from inside.

With officers initially unable to determine what had happened inside, police backed away, established a perimeter and treated the home as a barricaded situation.

Nearly two hours later, officers breached the front door.

Inside, they discovered a devastating scene, with Williams, George and all four children dead from gunshot wounds.

Investigators also believe the final gunshot heard by the arriving officer was Williams taking his own life.

But the news conference also revealed that Tuesday's massacre was not law enforcement's first encounter with Williams.

DeLong said officers had dealt with Williams over "erratic behavior," including contact as recently as within the previous few weeks.

Police had also received calls involving aggressive behavior in public and reports of gunfire, although DeLong said investigators had been unable to determine the source of the reported shots.

Williams’ behavior had raised enough concern to put him on law enforcement's radar, but DeLong said nothing officers encountered suggested he was on the verge of killing his family.

The disturbing killings came after decades of brushes with the law for Williams, who operated under a long list of aliases and whose criminal history included a felony sex offense and a requirement to register as a sex offender in Kansas.

Williams appeared on the Kansas Bureau of Investigation's sex offender registry under the name Freddie Lu'Carl's Williams, with "Ronald Williams" among numerous aliases listed by the state.

His encounters with the criminal justice system stretched for nearly three decades.

Court records reviewed by KCTV showed Williams faced felony charges involving drugs, battery, assault on a law enforcement officer, burglary, attempted rape and kidnapping, among other alleged crimes, in cases dating from 1995 through 2024.

The charges spanned multiple jurisdictions, including Wyandotte, Johnson and Franklin counties, according to KCTV.

For those who lived just steps from the family, the killings left behind shock, heartbreak and haunting questions about whether something had been missed.

Ann Stofferan, who lives only a couple of houses from the scene, told KWCH that learning children were among the dead made her "stomach churn."

"I just felt so sad and heartbroken for that family," Stofferan told the outlet. "Because I just can't imagine what that man was thinking to do that. I just can't."

Another neighbor offered an especially haunting recollection, telling KWCH she remembered hearing Williams make an ominous statement to his wife before the killings.

"I remember him telling his wife, 'I'm going to do it, I'm going to do it, I'm going to call the cops, and I'm going to do it,'" the woman told the outlet.

She said she did not know at the time what Williams allegedly meant.

"How do you kill your own family? How do you do that? I just don't get it," she said.

Tonya Asbury, who lives about a block away, told KWCH the killings left her wondering whether something could have been done before five lives were lost.

"I hate to say it, but somebody failed," Asbury said. "Somebody in this community failed that family. Failed him and that family."

Investigators have not publicly identified a motive for the killings.

The scene had a profound impact on the officers and investigators who responded, with peer-support teams and mental health professionals called in to help them process what they encountered.

For DeLong, the scale of the killings was unprecedented during his career in the community.

"In my 20-plus years here, no, I can't remember anything remotely close to this," DeLong said.

The KBI and Winfield Police Department are continuing to investigate.