HARRISBURG, Pa. — After weeks of anticipation , perhaps the most crucial witness in the Jerry Sandusky child sex abuse case roiling Penn State took the stand and told what he saw after he entered a campus locker room one night in 2002 and heard the sound of skin slapping on skin in the showers.

Mike McQueary, a towering, red-headed former quarterback who grew up in the Penn State hometown known as Happy Valley and led the Nittany Lions to the 1998 Citrus Bowl, is for now the only witness to testify publicly that Sandusky molested and perhaps raped a boy.

He is an unusual weapon for state prosecutors: Sexual assaults usually don't have an adult eyewitness willing to testify. In addition, he may be the only witness who testifies against all three of the men who have been charged in the scandal.

While state prosecutors are prepared to have a number of accusers testify against Sandusky, McQueary's testimony is the linchpin in their contention that Penn State officials at the highest levels of the institution failed to protect children from a predator. That allegation has brought shame to a school whose sports programs vow "success with honor" and spurred trustees to oust Hall of Fame coach Joe Paterno and the school's longtime president, Graham Spanier.

On Friday, McQueary, 37, testified for two hours in a preliminary hearing for two Penn State administrators accused of lying to a grand jury about what McQueary told them about what he allegedly saw the football team's one-time defensive coordinator doing with a boy.

A chair and microphone in a packed courtroom was a much different public arena than the one he has long been used to as Paterno's right-hand man, wide receivers coach and recruiting coordinator, shadowing the coaching legend on the sidelines during football games.

Wearing a crisp dark blue suit and light blue tie, McQueary answered questions quickly and confidently, never seeming to wither or tire under rapid and repetitive questioning from defense lawyers.

Whether his testimony will cement the case for prosecutors is another matter.

McQueary's testimony will be useful at Sandusky's trial, lawyers not connected to the case say.

"In any kind of case about molestation, in any kind of sexual assault, generally, there's very, very seldom an eyewitness to the act itself," said Bruce Antkowiak, a former federal prosecutor who teaches law at Saint Vincent College in Latrobe, Pa. "Normally, the corroboration of the act is done with scientific evidence, if it's available, so yeah, this would be critical."

Sandusky maintains that he is innocent and waived his preliminary hearing this week. Prosecutors, however, say McQueary was prepared to testify at that hearing and would likely be a witness at the trial.

Prosecutors said Friday they still haven't identified the boy in the shower — one of 10 that Sandusky is accused of showering with, fondling, molesting or raping over a span of 15 years — but the lawyers say a victim is not necessary for a witness' testimony to convince a jury that the crime happened.

There might be a caveat. The grand jury report issued Nov. 5 paraphrased McQueary's testimony as saying he saw a boy in the shower "being subjected to anal intercourse" by Sandusky.

In his testimony Friday against university officials Tim Curley and Gary Schultz, McQueary said he could not be 100 percent sure that Sandusky was raping the boy, but that he was sure something of a sexual nature was happening.

"That key point is helpful to us," Sandusky lawyer Karl Rominger said.

It's interesting that McQueary appeared to have moved away from the graphic description mentioned in the grand jury report, Rominger said, and shows that the grand jury report is arguably overblown.

But, Rominger added, defense attorneys still haven't had a chance to review a transcript of McQueary's grand jury testimony and it's possible that McQueary didn't use the exact graphic wording in the grand jury report, which is written by prosecutors.

Others weren't so sure it will make a difference if it comes across as a slight difference in recall or rendition by a witness.

"In real life, it is only when the witness changed a material part of their story that it seems to have an impact on the jury," Antkowiak said. "That's far more compelling, I think, than pointing out an inconsistency in how they told the story."

Defense attorneys for Curley, the athletic director who has been placed on leave, and Schultz, a senior vice president who returned to retirement after spending about four decades at the school, seemed keenly interested in how McQueary reacted to what he saw in the shower.

He left the boy in the shower with Sandusky, one pointed out. He didn't fill out a police report — although he testified that he thought reporting it to Schultz was like reporting it to campus police since the police director reported to Schultz. Curley and Schultz didn't tell him not to tell anyone about it. He never told Curley and Schultz that he was dissatisfied with how they responded to what he told them. And he never tried to find out who the boy in the shower was.

"All those questions legitimately raise the question, 'Did he actually see that?' because he didn't act like a man who did," said Bruce Ledewitz, a former public defender who teaches criminal law at Duquesne University in Pittsburgh.

For his part, McQueary says he was shocked, horrified and distraught at what he saw. He had played for Penn State when Sandusky was the team's defensive coordinator, and even played football on teams with Sandusky's adopted sons.

McQueary testified that he never used a word like "crime" or "sodomy" or "assault" to describe what he saw Sandusky doing in the shower with the boy, but was adamant that he left Curley and Schultz with the strong impression that something sexual and certainly inappropriate and "over the lines" had happened.

Regardless, McQueary's testimony was good enough for District Judge William C. Wenner to decide that prosecutors had met the burden of proof to send the case against Schultz and Curley to a jury trial.

Influencing a jury at trial is an entirely different exercise.

For one thing, it's very hard to prove perjury: Prosecutors must show that Curley and Schultz knew they were lying, lawyers say.

"Somebody testifies to something that is not accurate? That happens every day in every trial, in every case," said Pittsburgh personal injury and criminal defense lawyer James E. DePasquale. "That does not amount to perjury. You would have to be able to show that they testified to something that is not accurate intentionally, in order to mislead."

So McQueary's description of what he saw may be vague enough for jurors to decide that Curley and Schultz were left with the impression they gave to jurors: The conduct didn't sound serious or like a crime, and they didn't report it to police.

McQueary's use of language "seems to corroborate to me, to a certain extent, what the defendants have said he said to them," Ledewitz said.

Asked whether the case will hinge on the fact that McQueary never used a word like "sodomy" or "rape," Senior Deputy Attorney General E. Mark Costanzo questioned whether McQueary should be blamed for another adult's failure to act.

"It's a sad, sad, sad day when you think about all of these victims and you just got your first taste of it today and you saw the inaction by a number of ... supposedly important, responsible adults," Costanzo said after the judge's decision to send the case to trial. "And there was a lot of inaction in this case."

Associated Press writers Maryclaire Dale in Harrisburg and Joe Mandak and Kevin Begos in Pittsburgh contributed to this report.