Inmate testifies he overhead Jack McCullough say he killed 7-year-old Maria Ridulph in 1957

(CBS/AP) SYCAMORE, Ill. - An inmate testified Wednesday that he overheard the man accused in the 1957 slaying of 7-year-old Maria Ridulph tell another cellmate that he choked the Illinois girl to death with a wire.

The testimony came on the third day in one of the oldest cold-case murders to go to trial in the U.S. Jack McCullough, a 72-year-old former Washington state police officer, has pleaded not guilty to abducting and murdering the girl more than 50 years ago.

Christopher Diaz, who was incarcerated at the same jail as McCullough while the murder suspect awaited trial, told the court he also heard McCullough boast that he had brushed aside an offer from the state to cut a plea deal.

Diaz, charged in a separate case, insisted prosecutors did not offer him anything for his testimony.

Maria Ridulph disappeared on Dec. 3, 1957 and her badly decomposed body was found about 120 miles from Sycamore in the spring of 1958.

Also on Wednesday, forensic anthropologist Krista Latham testified that an examination of the girl's exhumed remains last year suggested she was stabbed in her chest and throat area.

The girl's bones had cut marks consistent with a large-bladed knife, Latham said. She testified that they did not appear to have come from an autopsy scalpel or saw, through she conceded it was at least possible the marks were made in the initial autopsy.

McCullough lived a few blocks from the Ridulph family home in 1957 and was on an early list of suspects. But he had an alibi, saying that on the day the girl vanished, he traveled to Chicago to get a medical exam before enlisting in the Air Force. Investigators reopened the case a few years ago, after McCullough's former girlfriend told them she found his unused train ticket from Rockford to Chicago from Dec. 3, 1957, the day Maria vanished.

The defense opted for a bench trial, meaning a judge will decide the verdict.