Opening statements got underway in the long-delayed criminal trial against Spanier, who faces felony charges of child endangerment and conspiracy for how he handled a 2001 report that the former assistant football coach had abused a boy in a team shower.
Sandusky, a former assistant football coach, was convicted in 2012 of sexually abusing 10 boys and is serving decades in prison.
On Monday, seven women and five men were chosen for the main jury panel after questioning of prospective jurors was done in secret. Four alternates were picked Tuesday morning.
Deputy Attorney General Patrick Schulte told jurors that Spanier and others agreed not to report Sandusky and, as a result, "evil in the form of Jerry Sandusky was allowed to run wild."
The attorney general's office's witness list includes two former Penn State officials who took plea deals in the case last week - former vice president Gary Schultz and former athletic director Tim Curley.
It also includes a former Penn State lawyer, the onetime head of a charity for children founded by Sandusky, police and someone described only as "a confidential witness." Another potential witness is Mike McQueary, a graduate assistant coach who reported seeing Sandusky shower with the boy.
Defense attorney Sam Silver disputed any notion that his client and others didn't respond to the 2001 complaint about Sandusky.
"They made a decision they believed was appropriate under the circumstances," he said, accusing prosecutors of trying to "criminalize a judgment call."
Schulte told jurors about a May 1998 incident in which mother reported Sandusky showering with her son, and said Schultz informed Spanier "because the president of the university should be apprised of something like that."
After a month the investigation ended with no charges being filed.
After McQueary's 2001 report, Spanier, Schultz and Curley decided to talk to Sandusky and bar him from campus rather than report him to child-welfare authorities, Schulte said. They told him if he didn't get help they would report him, he said.
"Gary Schultz is going to tell you that he is very regretful of the decision to not be firmer in insisting that they go to" state child-welfare authorities, Schulte said.
The trial is expected to last about a week.
Spanier, 68, was forced out shortly after Sandusky was charged with child molestation in 2011. Sandusky was sentenced to 30 to 60 years in prison and maintains his innocence.
Schultz and Curley had faced the same charges as Spanier before they pleaded guilty last week to a single misdemeanor count of child endangerment, and they await sentencing.
Silver took issue with the conspiracy charge, saying Penn State officials told a few other people about the complaint and reported Sandusky to Second Mile, a charity Sandusky founded and where he met most of his victims.
"That's a heck of a way to pull off a conspiracy to endanger the welfare of children, to go off and tell all these people," he said.
The charges stem from their handling of the 2001 report from McQueary that Sandusky had apparently molested a boy in a team shower. Prosecutors say their failure to report that to authorities allowed Sandusky to continue to abuse boys and also endangered others.
Spanier has said that Curley and Schultz characterized the incident in the shower as horseplay and not any form of child abuse. He denies any wrongdoing.
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