Orlando Williams, 39, was sentenced Monday to life in prison without parole for killing his fiancee's eight-year-old son

A Pittsburgh man has been found guilty of killing his fiancee's eight-year-old son by slamming him onto the floor for not cleaning his room.

Thirty-nine-year-old Orlando Williams was sentenced Monday to life in prison without parole.

He was charged with homicide and child endangerment counts in the June 2016 death of the JonMarquis Stepich, who suffered critical head injuries.

Authorities allege Williams had been drinking and tripped over a laundry basket in the boy's room.

They say he then angrily tried to slam the boy onto the edge of his bed but missed and slammed him onto the floor.

In court, the brutal details of JonMarquis' murder emerged. His head was banged on a flat surface 'over and over and over and over again', the Pittsburgh Post-Gazette reports.

The judge said that the only question was 'Did the defendant kill with specific intent?' and that she found 'beyond a reasonable doubt the answer is yes.'

A defense attorney previously argued the evidence presented wouldn't support a charge more serious than involuntary manslaughter. She said Williams acted as a 'father figure' to the boy for years and was 'inconsolable' over his death.

Williams slammed the boy, named JonMarquis, into the ground when he became angry after tripping over a laundry basket

Williams told police he meant to slam the boy on his bed, but JonMarquis fell

'My client is very satisfied with the verdict. It was very tragic what happened. Justice was definitely served today in the courtroom,' said Dan DeMarco, an attorney who represents JonMarquis' mother, Aliehsa Lininger.

Lininger is charged with endangering the welfare of children in the case.

She testified against Williams last week and told the court that he had been abusive to JonMarquis and her other son and that he often spanked them with belts and cords.

The boy's mother is charged with endangering the welfare of children in the case. Pictured: the family home

'His mom feels very relieved and safe now,' said Lininger's sister, Lauren Anthony.

JonMarquis had to be placed on a ventilator and suffered a brain bleed and herniated brain stem. He also had bruises covering his body, according to a criminal complaint.

Doctors called police after seeing the extent of the boy's injuries.

Williams and his mother took the boy to a nearby hospital. JonMarquis was then flown to the Children's Hospital of Pittsburgh, where he died three days later.