They had been divorced for four years, but the divorce decree permitted Sankey to stay in the same house, Carter said.
After killing the 42-year-old with a pistol, Sankey called friends and family members to confess and asked them to come over, but he refused to let anyone call 911, Carter said.
Union City police were not notified of the death until four hours after Williams left the 4700 block of Main Street.
Detectives learned the couple had a volatile relationship and argued over who would keep the house once they separated.
Family members told police Sankey had been having a hard time accepting the divorce. After hours of evading police on the night of the crime, he turned himself in.
Sankey was found guilty of felony murder, aggravated assault, cruelty to children, false imprisonment and possession of a firearm during the commission of a crime.
Sentencing is scheduled for a later date.