Barring an unexpected development, Mr. Bullock, now retired from the Edgefield County Sheriff's Office, will make good on that promise Friday, when South Carolina is set to execute Mr. Williams for the deaths of 39-year-old Linda Williams and 12-year-old Shaun Williams.
Their bodies were found in June 1991 in Sumter National Forest in Edgefield County, where they had been doused with gasoline and set ablaze in the family's van. The van had been driven into a tree in what police called a botched attempt to stage an accident. Mrs. Williams had been beaten to death, Shaun strangled.
Mr. Williams, of Evans, was arrested the next year after he tried to collect on $525,000 life insurance policies. Mr. Bullock, who spent hours interrogating him, says he never cooperated with investigators or expressed remorse.
"He never did get upset, he never did cry nothing like that," Mr. Bullock says. "He was very, very cold."
Now, authorities say, Mr. Williams has exhausted his state and federal appeals.
He has also sued over the legality of lethal injection, and a South Carolina federal judge denied his request to delay execution while that case goes forward. A federal appeals judge turned down Mr. Williams' appeal of that decision, and today his attorneys petitioned the U.S. Supreme Court to reconsider.
It was not clear when the high court would rule.
Mr. Williams, now 56, told authorities he last saw his family when they went shopping the morning their bodies were found.
Shortly after the deaths, Mr. Bullock said, Mr. Williams' plan became apparent: His disability money was about to run out, and his wife was planning to leave him and return to her parents in Florida.
Mr. Williams took out life insurance policies totaling more than half a million dollars on his wife and son, who had been orphaned in El Salvador's civil war.
"I think he panicked," Mr. Bullock says. "He decided to take his family out. ... I think he had a plan, but it wasn't ready. He found out she was leaving, so he had to act fast."
Mr. Bullock said he's ready to see Mr. Williams die.
"I told him I'd be there. I promised him I'd be there," Mr. Bullock said. "I just want to finalize it."