The investigation into alleged child sex abuse by a former Pennsylvania State University football coach expanded Thursday, as state authorities explored new allegations against Jerry Sandusky and Texas police opened a probe into claims he molested a boy there twice in the 1990s.

Pennsylvania state troopers have interviewed at least two new accusers since Sandusky's arrest last weekend and were girding for more, according to a source close to the case but unauthorized to publicly discuss it.

Police believe the national spotlight will spur more victims to break years of silence, much like Catholic church sex-abuse scandal did, the source said.

And Thursday night, the university announced that a key assistant coach who has been central to the case against Sandusky would not take part in Saturday's game against Nebraska because he had been the target of "multiple threats."

A day after the scandal led to the firings of head football coach Joe Paterno and university president Graham B. Spanier, the school and its fans struggled to recover from the most tumultuous stretch in Penn State history. The spotlight showed no signs of dimming.

A San Antonio police spokesman confirmed that detectives there were exploring charges against Sandusky for allegedly sexually abusing a boy during trips with Penn State's football team to bowl games in 1998 and 1999. "We are going to be taking what action we can to see if a case can be built," prosecutor Cliff Herberg told a local radio station, WOAI-AM.

The boy in that case is one of eight that Sandusky, 67, allegedly molested at his house, on campus, and on road trips between 1994 and 2008. He stepped down as Paterno's defensive coordinator in 1999 but maintained an office at the football complex and ties to the university through his foundation for underprivileged boys and camps it ran at Penn State.

Prosecutors have also charged two school administrators, athletic director Tim Curley and senior vice president Gary Schultz, with covering up an alleged 2002 campus assault by Sandusky and later lying about it to authorities.

All have denied the charges.

Thousands of students rushed into the streets after Paterno's abrupt ouster Wednesday after 46 years as head coach and sparked late-night clashes between police and journalists. Police said they were reviewing tapes and preparing charges.

But that didn't stem what has been a chorus of criticism about the alleged abuse and questions over whether the Paterno or others could or should have stopped it.

U.S. Sens. Patrick J. Toomey (R., Pa.) and Bob Casey (D., Pa.), both withdrew their nomination of Paterno for a Presidential Medal of Freedom, the highest civilian honor given by the White House. A spokesman for President Obama said the allegation regarding Sandusky and school officials, if true, "is outrageous."

The National Collegiate Athletic Association said it would investigate whether actions by Penn State officials violated its bylaws. NCAA president Mark Emmert told ESPN the Sandusky case was "easily the worst scandal" he had ever seen in college sports.

According to the grand jury, a graduate coaching assistant said he saw Sandusky raping a young boy in the team showers one night in 2002 and reported it to Paterno and other administrators.

No one passed the information to law enforcement, even though Sandusky had been investigated at least once before for alleged inappropriate conduct with a boy.

Paterno and Spanier have denied any wrongdoing. The graduate assistant, Mike McQueary, is now a receivers coach for the team.

McQueary has been the focus of increasing public scrutiny and criticism for not notifying law enforcement of what he had seen. Last night, the university reported he had been the target of threats. In a statement, the university said "it would be in the best interest of all for Assistant Coach McQueary not to be in attendance at Saturday's Nebraska game."

Paterno spent his first day out of coaching at home with his wife as reporters camped out front. A player and assistants dropped by.

His replacement, defensive coordinator Tom Bradley, said he would strive to "restore the confidence" in the program.

Spanier's replacement, Rodney Erickson, urged the community to stay calm. "The eyes of the nation are upon you," Erickson told students, faculty, and staff in a statement. "Please set an example that will make us all proud."

The university trustees met privately for a fourth time this week. At its public meeting Friday, the board is expected to name a special committee to investigate how the university responded to the allegations about Sandusky.

Emerging from the trustees meeting, Gov. Corbett said he supported the board's decision to oust Paterno and Spanier, saying he had lost confidence in both.

"When it comes to the safety of children, there can be no margin for error, no hesitancy to act," said Corbett, a trustee by virtue of his office. "Unfortunately, in my career, particularly as attorney general, I have seen many instances when people who have power believe they are beyond the law."

Contact staff writer John P. Martin at 215-854-4774, jmartin@phillynews.com, or @JPMartinInky on Twitter.

Inquirer staff writers Jake Kaplan, Amy Worden, and Joe Juliano contributed to this article.