Former Penn State vice president Gary Schultz, left, former president Graham Spanier and former athletic director Tim Curley.

Three former Penn State University administrators — former President Graham Spanier, former vice president Gary Schultz and ex-athletic director Tim Curley — were ordered Tuesday to stand trial on charges they covered up the Jerry Sandusky child sexual abuse scandal.

The three are due to be arraigned in Harrisburg, Pa., on Sept. 20.

A Pennsylvania district judge ruled Tuesday that prosecutors had shown enough evidence to warrant a trial.

Judge William Wenner called it "a tragic day for Penn State University," according to NBCPhiladelphia.com.

State prosecutors allege the three men didn't tell police about sexual abuse allegations involving former assistant football coach Sandusky and actually tried to cover up what they knew about it.

Sandusky was convicted in 2012 of 45 counts of child sexual abuse and is serving a prison sentence. He maintains his innocence and is appealing the conviction.

The three men claim they are innocent of wrongdoing, and say they were unaware of an allegation against Sandusky in 2001. They say they believed Sandusky and a young boy were engaged in nothing more than horseplay in a university locker room shower.

Mike McQueary, a former football team assistant, testified he saw Sandusky and a boy engaged in a sex act in the shower. He also said he reported the incident to coach Joe Paterno, Curley and Schultz. Paterno was fired and died in January 2012.

Curley and Schultz were initially charged in November 2011, when Sandusky was arrested, and accused of perjury and failure to properly report the incident.

Spanier was forced out as president at that time. He remains a faculty member on administrative leave.