A homeless Charleston man has been found guilty but mentally ill for sexually assaulting an elderly woman in 2011 who was dying in a Mount Pleasant hospice center, according to reports.

Calvin Williams, 56, was sentenced to 25 years in prison, WCBD-TV reported. If he ever faces parole, he'll be held indefinitely in a violent sexual predator program that will require him to demonstrate he no longer is a threat to society.

Read more about the case.

Police accused Williams of assaulting the 86-year-old woman in her room at Hospice Center of Charleston on Wando Park Blvd. in February 2011. A nurse walked in on the assault, according to a police report. Williams, who was reportedly homeless at the time, entered the facility through an unlocked door.

Williams opted for a bench trial, with guilt being decided entirely by Judge R. Markley Dennis. Williams has been in jail since his 2011 arrest. His criminal record dates back to the early 1980s with previous sex crime conviction.

The victim died from cancer eight days after the attack. The family settled a civil lawsuit against the hospice center's parent company in May, the Post and Courier reported.