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.