The man's lawyers said Thursday they have done an extensive investigation and gathered "overwhelming evidence" on details of the abuse by Sandusky, the former assistant football coach convicted of using his position at Penn State and as head of a youth charity to molest boys over a period of 15 years.
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Jurors convicted Sandusky last month of offences related to so-called Victim 2 largely on the testimony of Mike McQueary, who was a team graduate assistant at the time and described seeing the attack.
"Our client has to live the rest of his life not only dealing with the effects of Sandusky's childhood sexual abuse, but also with the knowledge that many powerful adults, including those at the highest levels of Penn State, put their own interests and the interests of a child predator above their legal obligations to protect him," the lawyers said in a news release.
They did not name their client, and The Associated Press generally does not identify victims of sex crimes without their consent.
The university said it was taking the case seriously but would not comment on pending litigation.
University President Rodney Erickson and the board of trustees, a school spokesman said, "have publicly emphasized that their goal is to find solutions that rest on the principle of justice for the victims."
The statement from the man's attorneys said Victim 2 suffered "extensive sexual abuse over many years both before and after the 2001 incident Michael McQueary witnessed."
McQueary testified in December at a hearing that he had seen Sandusky and a boy, both naked, in a team shower after hearing skin-on-skin slapping sounds.
"I would have described that it was extremely sexual and I thought that some kind of intercourse was going on," McQueary said.
McQueary reported the abuse to school officials, including coach Joe Paterno, but none of them told police. In a recent report conducted by former FBI Director Louis Freeh and commissioned by Penn State, the investigators excoriated Paterno and the other administrators for not attempting to identify Victim 2, saying it showed "a striking lack of empathy."
Trustees fired Paterno, who has since died, because he failed to do more about claims against Sandusky, and the scathing independent review said several top school officials looked the other way because they were afraid of bad publicity. The NCAA has vacated 112 Penn State wins.
In a pair of voicemails recorded last year, released with the statement and posted online by the lawyers, a voice that's purportedly Sandusky's expresses his love and says he wants to express his feelings "up front."
The voicemails are dated Sept. 12 and Sept. 19, less than two months before the former Penn State coach was arrested on child sex abuse charges. Sandusky was convicted in June of 45 sex abuse counts and awaits sentencing.
The second voicemail asks whether Victim 2 would like to attend Penn State's next game.
Sandusky left "numerous" voicemails for their client that fall, the attorneys said.
Before the trial, defence attorney Joe Amendola said he had met with a man he believed he might be Victim 2 and the man told him he had not been abused by Sandusky. Amendola said he was not convinced and did not intend to subpoena him, but also said Sandusky himself was insistent they had the right person.
The statement from Victim 2's lawyers leaves many questions unanswered, including whether he had been in contact with prosecutors before or during the trial, whether he remembers McQueary, and whether he is the same person who met with Amendola.
"Jerry Sandusky's abuse of Victim 2 and other children is a direct result of a conspiracy to conceal Sandusky's conduct and the decisions by top Penn State officials that facilitated and enabled his access to victims," the statement read. "We intend to file a civil lawsuit against Penn State University and others and to hold them accountable for the egregious and reckless conduct that facilitated the horrific abuse our client suffered."
The statement did not say when the lawsuit would be filed or contain details on what redress the plaintiff is seeking. The lawyers said they would not have further comment, and messages left for their spokesman were not immediately returned.
Several messages seeking comment from Amendola and Sandusky's other lawyer, Karl Rominger, were not immediately returned.
Prosecutors had said on several occasions they did not know the identity of the boy, and they offered no reaction to the lawyers' announcement Thursday.
"We can't comment, given both our ongoing criminal prosecutions and our ongoing investigation," said Nils Frederiksen, spokesman for the attorney general's office.
The lawyers who released the statement include several based in Philadelphia and in State College, home to Penn State's main campus — where the shower assault took place. They also represent three other young men Sandusky was convicted of abusing but have not filed any lawsuits.
A second accuser has filed paperwork indicating an additional complaint is in the works, while other lawyers also have indicated they represent young men with potential claims.
This week Penn State's general liability insurer sought to deny or limit coverage for Sandusky-related claims. Pennsylvania Manufacturers' Association Insurance argued that Penn State withheld key information needed to assess risk.
In June, after Sandusky was convicted, the university said it hoped to quickly compensate victims and would reach out to their lawyers. Penn State spokesman Dave La Torre declined to comment on anything related to the victims and any settlement discussions.
Lawyers' statement and voicemails: http://bit.ly/NYmGvl
Associated Press writer Maryclaire Dale in Philadelphia contributed to this report