A Burnsville man accused of killing his girlfriend's son in 2013 pleaded guilty Wednesday to second-degree murder in the death of 4-year-old Key'ontay Miller Peterson.

The plea agreement calls for William Alphonso Warr, 26, to be sentenced to 30 years in prison, according to the Dakota County attorney's office.

"We are pleased to have brought William Warr to justice for this violent crime, which claimed the life of a defenseless child," Dakota County Attorney James Backstrom said in a statement.

Key'ontay died from complications of blunt-force trauma on June 11, 2013, according to the Hennepin County medical examiner. A tear in Key'ontay's small intestine led to sepsis, and an autopsy showed that his body was covered with bruises and adult bite marks. The boy also had several broken ribs.

Warr was charged with eight counts of first- and second-degree murder last year, and jury selection for his trial was underway when he pleaded guilty. The count to which Warr pleaded guilty acknowledged that he was under a restraining order when he killed Key'ontay.

A 30-year sentence would be an upward departure from state sentencing guidelines because of the "particular vulnerability" of the victim, according to Backstrom's office. Warr's sentencing is set for June 9.

On June 19, prosecutors are expected to seek a six-year sentence for Key'ontay's mother, Sha'reese Miller, who pleaded guilty in March to felony manslaughter for her role in the boy's death.

At her March plea hearing, Miller said she allowed Warr to be around her and the children despite having filed a protection order against him. She said she left Key'ontay alone with Warr even though she knew he had repeatedly assaulted the boy and her family had warned her that Key'ontay was in danger.

Key'ontay was part of a special report on child protective services last year by the Star Tribune.

The boy had told his mother, day care providers and other family members that Warr punched him in the stomach, gave him a black eye and whipped him with a belt.

Day care workers and family members reported the abuse to child protection in Hennepin County and later Dakota County after Miller and her children moved to Burnsville in May 2013. Each report was closed after Miller denied there was any abuse.

Warr has 2010 and 2012 convictions for felony domestic assault. He was sent to prison in July 2013 after pleading guilty to violating a protection order and several other charges related to attempts to flee police when they went to the Burnsville townhouse where Key'ontay died.

Stephen Montemayor • 952-746-3282