A former Illinois sheriff’s deputy who shot and killed a Black woman at her home after she called 911 died on Sunday while serving a 20-year murder sentence.

Sean Grayson, 32, who was white, was found guilty in October of second-degree murder in the 2024 killing of Sonya Massey, a rare instance of an American law enforcement officer convicted of a crime in an on-duty shooting.

He was sentenced in January and had been in prison for just over six months when he died.

His lawyer, Daniel Fultz, confirmed his death but declined to provide any further details.

Mr. Grayson had applied for medical release but was unanimously denied by the Illinois Prisoner Review Board last month. The Illinois Department of Corrections did not immediately return a request for information.

During his sentencing, Mr. Grayson’s lawyers said he had colon cancer that had spread to his liver and lungs, and they urged Judge Ryan Cadagin for leniency. Judge Cadagin instead gave Mr. Grayson the maximum sentence allowed.

Ms. Massey, who was 36, had called 911 for help in July 2024 because she was worried someone was lurking outside her house near Springfield, Ill.

Mr. Grayson and another deputy responded to the call, and after looking through the yard, found no one hiding. They then knocked on Ms. Massey’s front door, spoke with her and stepped inside.

The conversation was amiable until Ms. Massey moved to remove a pot of hot water from her stove. After picking up the pot, she said, “I rebuke you in the name of Jesus.”

The encounter quickly escalated, and Mr. Grayson told Ms. Massey to drop the pot, threatening to shoot her in the face if she did not. Within seconds, the deputies had pulled their guns, and Mr. Grayson fatally shot Ms. Massey in the head.

Illinois State Police released body camera footage of the exchange.

The day before the shooting, Ms. Massey’s mother had called 911 and told the dispatcher that her daughter was having mental health issues.

Mr. Grayson told the jury in October that he had feared for his safety when Ms. Massey lifted the pot of hot water, and that the only tool he had to stop the threat was his weapon. Prosecutors argued that he had needlessly escalated the situation.

The Sangamon County Sheriff’s Office fired Mr. Grayson shortly after the shooting. The other deputy in the encounter, who had tried to stop Ms. Massey’s bleeding after she was shot, was not charged.

The Justice Department later opened an investigation, telling officials in Sangamon County that the shooting raised “serious concerns” about the way the sheriff’s office interacted with Black people and people with behavioral health disabilities.

In January, the agency said it had found no discriminatory practices behind the fatal shooting.