Joshua Dall-Leighton, the former prison guard who was celebrated for donating a kidney to a stranger but is now accused of sexually assaulting a female inmate in his charge, pleaded not guilty Monday in York County Superior Court to the five felony counts, the clerk’s office said.

An affidavit filed in York County Superior Court by Maine Department of Corrections investigator David P. Verrier describes several sexual encounters that allegedly took place between the corrections officer, Dall-Leighton, 31, of Standish, and the 31-year-old inmate.

The encounters are alleged to have taken place in the prison transport van owned by the Southern Maine Re-entry Center in Alfred, where Dall-Leigton worked. Dall-Leighton drove the van, using it to transport the female inmate to her workplace in Sanford. The encounters in the van occurred in various locations in Wells and Sanford, according to the affidavit.

On Nov. 9, the York County grand jury indicted Dall-Leighton on five counts of gross sexual assault and one count of unlawful sexual contact. The indictment says Dall-Leighton had “supervisory or disciplinary authority” over the inmate. If convicted, he could face up to 10 years in prison.

Dall-Leighton is no longer working at the pre-release center because he is facing criminal charges, his court-appointed attorney said. The attorney, Neal Weinstein of Old Orchard Beach, has said there was no force used by his client, and framed the case as a contest of credibility between an accuser who is a convicted felon and his client, who has no criminal record.

According to the State Bureau of Identification, the female inmate was convicted in January 2012 in Rockland of elevated aggravated assault, robbery and burglary. She was sentenced to 10 years in prison with four years suspended. The Portland Press Herald does not identify victims of alleged sexual assault without their consent.

Dall-Leighton received local and national media attention in 2015 when he responded to a plea written on a car window from a woman who was looking for a kidney donor. He turned out to be a match for the woman, Christine Royles of South Portland.

Royles was diagnosed in 2013 with lupus and an autoimmune disease, ANCA vasculitis. She had entered permanent kidney failure, but rather than languish on a national waiting list, Royles painted the sign on her car window. The transplant was successfully performed in June 2015 at Maine Medical Center in Portland.

The affidavit filed by Verrier prison officials found a letter the victim had written to a Bangor attorney who represented another female inmate.

“I avoided sexual intercourse with this officer for some time but because of his position of power, and the many things I stood to lose, I felt pressured to engage,” the alleged victim wrote. “This officer transported me to work several times per week and we were often alone while driving. I requested a job change, but was repeatedly denied. I felt I was in a no-win situation.”