DENVER -- A former Denver school teacher and Episcopal priest accused of sexually assaulting at least two boys in his Denver home was sentenced Thursday morning to 24 years in prison.

Donald Shissler, 68, pleaded guilty to the charges in August as part of a plea bargain.

He was originally charged with two counts of sexual assault on a child, two counts of sexual assault on a child by a person in a position of trust, one count of sexual assault on a child -- pattern of abuse, and one count of sexual exploitation of children.

In a deal with prosecutors, Shissler pleaded guilty to two charges of sexual assault on a child, and the other counts were dismissed.

But investigators said that this isn't necessarily the end of Shissler's case.

Based upon evidence found in his home earlier this summer, there may be as many as 20 additional victims, detectives said. Police said they seized hundreds of pornographic pictures and videos from Shissler's house when he was arrested.

A spokeswoman for the Denver district attorney said that more alleged victims of Shissler spoke at his sentencing Thursday morning, saying that they were sexually assaulted by him.

Calling his crimes "incomprehensible," judge Sheila Rappaport gave Shissler the maximum sentence possible -- 12 years for each sex assault.

Rappaport concluded in her sentencing remarks that Shissler is a sexual predator who clearly committed crimes against young boys for almost 18 years, including sexually assaulting a boy he adopted.

Prosecutor Kerri Lombari called Shissler's case "the most disturbing case I have ever worked as a prosecutor."

Shissler was an Episcopal priest for two years, last serving in Aspen in 1963. He also taught at North High School from 1984 to 1994, and was a foster parent in the 1980s.