McCullough was convicted in September in one of the oldest unsolved crimes in American history to make it to trial. Life in prison was the maximum sentence he faced.
The sentencing took place in Sycamore, the small community where 7-year-old Maria Ridulph was abducted and killed in December of 1957. It's the justice Maria Ridulph's family members said they've waited for.
"Even after 55 years, people can be brought to justice," Charles Ridulph, Maria's brother, said.
McCullough was sentenced to natural life in prison on Monday for the 1957 murder, kidnapping and abduction of Ridulph.
"It's justice for Maria and it's justice for the Ridulph family," Brion Hanley, investigator, said.
"He's still the same person today that he was back in 1957 when he kidnapped and murdered Maria," Julie Trevarthan, former McCullough prosecutor, said. DeKalb County Prosecutor Victor Escarcida called McCullough "the definition of evil."
Maria Ridulph was last seen on December 3, 1957, near her rural home. Her remains were found five months.
She had been playing with friend Kathy Chapman and a 17-year-old boy called "Johnny" when Maria Ridulph disappeared. Chapman identified McCullough as the 17-year-old who went by the name John Tessier in 1957.
"It's a sense of relief. Finally, it's run its course and we've put it to rest," Chapman said.
McCullough was arrested in 2011 in Washington State after one of his half-sisters came forward and told police about a death bed confession their mother made in 1994.
"Our family just wants to express our deep sadness that this tragedy had to go on for so long and this secret had to be kept for so long," Mary Hunt, McCullough's half-sister, said.
In court, McCullough did not repent. He was admonished by Judge James Hallock for turning to face Ridulph's family and friends while proclaiming his innocence.
"I did not, did not, kill Maria Ridulph. It was a crime I did not, would not, could not have done," McCullough said.
Despite the plea, McCullough received the maximum sentence. He also received five years for kidnapping and seven years for abduction.
McCullough's attorney said his client will appeal. He said that a box of FBI documents could prove McCullough's alibi that he was not in Sycamore on the day Maria Ridulph disappeared. Judge Hallock ruled those document inadmissible because the people mentioned in the documents were dead and could not be cross-examined.
"And when God has got everything in control, it's really hard to waste time thinking or worrying about it," Pat Quinn, Maria's sister, said.