DANVILLE, Ill. (WCIA) — A 78-year-old man has been sentenced to 20 years in prison after he pleaded guilty in Vermilion County on Monday to sexually assaulting his intellectually underdeveloped great-niece.

In a press release, State’s Attorney Jacqueline Lacy said Roger Deckard was accused of tricking the victim into having various sexual encounters with him. Lacy said Deckard took advantage of the victim’s underdeveloped maturity and her trusting nature when committing these crimes.

Family members subsequently discovered the crimes and contacted law enforcement, which included authorities in both Vermilion County and Indiana. The victim told authorities about Deckard’s actions and Deckard himself confessed his behavior to his family.

“Those individuals that prey on our disabled adults of Vermilion County will not be tolerated and my office will do everything in our power to bring those perpetrators to justice and that our disabled adults and children are kept safe,” Lacy said.

Deckard was charged with two counts of criminal sexual assault, each of which he was sentenced to 10 years in prison for. Those sentences will be served consecutively and he must serve at least 85% of each sentence. Following his release from prison, Deckard will have to serve parole from anywhere between three years to the remainder of his life.

The victim’s mother was present at Deckard’s sentencing, accompanied by victim advocates from Lacy’s office and representatives of the Survivor Resource Center.