A source familiar with the state investigation of child sexual-assault allegations against former Penn State defensive coordinator Jerry Sandusky tells ESPN's Tom Rinaldi that Mike McQueary stopped Sandusky's alleged rape of a boy as young as 10 years old that McQueary witnessed in 2002.

The source characterized McQueary, a key witness in the case, as "credible" and "consistent" in describing the events of the alleged attack at a shower at the Penn State practice facility to investigators.

McQueary, a Penn State wide receivers coach who was placed on administrative leave Friday, also told a friend in an email that he stopped the alleged rape and discussed it with police.

In the email, first obtained and reported Tuesday by The Morning Call of Allentown, Pa., McQueary said he "did have discussions with police and with the official at the university in charge of police" after the alleged incident.

In the email, dated Nov. 8, McQueary said, "I did stop it, not physically, but made sure it was stopped when I left that locker room," The Morning Call reported.

McQueary declined to be interviewed, and a message to his lawyer was not returned, the newspaper reported. State College police did not return a call seeking comment, according to the report.

Wednesday, in a brief off-camera meeting with ESPN's Lisa Salters, McQueary again said he wouldn't comment. When Salters said that people were looking to hear from him, McQueary said: "I understand -- I just can't right now."

In a brief interview with CBS News on Tuesday, McQueary said little.

"This process has to play out. I just don't have anything else to say," he said. Asked about his emotional state in the past week, he said: "All over the place. Just kind of ... shaken."

The former Penn State quarterback has faced immense criticism for not calling police, interrupting the alleged assault or, in the nine years since he was an eyewitness, demanding answers about why Sandusky was never charged.

Sandusky has been charged with molesting eight boys in 15 years, with some of the alleged abuse taking place at the Penn State football complex. He maintains his innocence and made his case in a national television interview Monday night on NBC.

Sources say the case "has generated multiple leads" and "information from the public" that has required state police to commit additional investigative resources.

In the email, McQueary wrote he "is getting hammered for handling this the right way or what I thought at the time was right," The Morning Call reported.

The Patriot-News of Harrisburg reported that McQueary is consulting with a Harrisburg law firm that specializes in employment issues to represent him in the ongoing investigation.

McQueary testified in a grand jury investigation that eventually led to child sex-abuse charges being filed against Sandusky. The ensuing scandal brought down longtime coach Joe Paterno, who was fired by university trustees Nov. 9 amid growing criticism that he should have done more to stop the alleged abuse. University president Graham Spanier was also dismissed.