Matt Sandusky, now 33, said the abuse started at age 8, a decade before he was adopted by the once-heralded defensive coordinator, according to the interview, first reported Tuesday by NBC News.
''If you were pretending you were asleep and you were touched or rubbed in some way, you could just act like you were rolling over in your sleep, so that you could change positions,'' Matt Sandusky said in an excerpt played Tuesday on NBC's ''Today'' show. His attorneys confirmed the recording's authenticity to The Associated Press.
Jerry Sandusky was convicted last week of 45 counts of abusing 10 boys he met through the charity he founded - the same organization that introduced him to Matt Sandusky, who became his foster child. Jerry Sandusky's principal lawyer did not return messages Tuesday, and another lawyer said only that Matt Sandusky's allegations contradict testimony he gave to the grand jury whose charges put his father on trial.
Matt Sandusky did not reveal any abuse when he was initially questioned as a grand jury witness but did release a statement alleging past abuse as the jury was sequestered in deliberations last week.
The police interview tapes are the first time Matt Sandusky's allegations of sexual abuse have been publicly aired, and too much time has passed for criminal charges. Asked why he was now coming forward on abuse purported to have occurred as early as the late 1980s, Matt Sandusky told police there were several reasons - but singled out his family.
''So that they can really have closure and see what the truth actually is. And just to right the wrong, honestly, of going to the grand jury and lying,'' he said in the police interview.
The AP does not identify people alleging sexual assault without their consent. Matt Sandusky's lawyers named him in a statement released Tuesday to reporters that acknowledged the tapes' validity.
''Although the tape was released without Matt's knowledge or permission, it illustrates that he made the difficult decision to come forward and tell the painful truth to investigators despite extraordinary pressure to support his father,'' lawyers Justine Andronici and Andrew Shubin wrote.
Jerry Sandusky hasn't been charged with abusing Matt, one of six children adopted by the former coach and his wife, Dottie. Messages left for Sandusky's other children were not returned.
Matt Sandusky sat with Dottie Sandusky on the first day of the trial but left after hearing one of the accusers testify. His attorneys have said he reached out to them while the trial was under way, saying he wanted to talk to prosecutors.
Matt Sandusky said that he was undergoing therapy and that his memories of abuse were only now surfacing. He said on the tapes that he tried to flee Sandusky's house and also attempted suicide.
''I know that I really wanted to die at that point in time,'' he said.
On the recording, Matt Sandusky says he was sexually abused off and on between ages 8 and 15. While being questioned, he said Jerry Sandusky would blow raspberries on his stomach and touch his genitals. The acts described were similar to accounts relayed by eight accusers who offered graphic testimony on the witness stand.
Those eight accusers said they met Sandusky through The Second Mile, the charity Jerry Sandusky founded for at-risk youth. Matt Sandusky also met his adoptive father through the charity.
Asked whether he recalled engaging in oral sex or being raped by the former Penn State coach, he told police ''at this point I don't recall that.''
Unless he recovers memory of rape or deviate sexual intercourse, it doesn't appear Jerry Sandusky could still be charged in connection with the allegations by his son.
State Attorney General Linda Kelly said Friday after the verdict that the investigation was continuing. Matt Sandusky's abuse allegations date as far back as the late 1980s, about a decade before the allegations on which Jerry Sandusky was tried.
If the abuse ended by 1995, Matt Sandusky's deadline for pressing criminal charges appears to have expired in 2003 for rape or involuntary deviate sexual intercourse, and in 2000 for lesser sexual abuse, according to sex-crimes prosecutors.
Until 2002, Pennsylvania law allowed accusers to report the most serious charges of sexual abuse until age 23 and lesser charges until age 20. The law was then changed to give accusers up to age 30 to come forward for rape or involuntary deviate sexual intercourse.
The law was extended again in 2007 to age 50 for all sexual abuse claims. But the changes are not retroactive - meaning Matt Sandusky would not be able to press criminal charges at this point.
On the civil side, Matt Sandusky may have missed his window for seeking damages from Penn State or others.
In Pennsylvania, accusers must now file lawsuits by age 30 in most cases, though exceptions are theoretically possible in the event of concealment or fraud.
''On the face of it, he's too late ... unless there's an exception around it,'' said lawyer Jeff Anderson, who filed the first lawsuit against Penn State over other Sandusky allegations. His client is not part of the criminal case because he came forward after the charges were filed.
Jerry Sandusky, 68, is under observation at the Centre County jail, where he has been separated from other inmates pending a psychological review to help determine the next step toward his sentencing in about three months. He has steadfastly maintained his innocence.
The son was prepared to testify against his father, lawyers have said. Defense attorney Joe Amendola has said that prosecutors told the defense that if Jerry Sandusky took the stand, Matt Sandusky would have been called as a rebuttal witness.
Another defense attorney, Karl Rominger, told the AP he and Amendola heard the tape before deciding not to put Jerry Sandusky on the stand.
He said that Matt Sandusky, on the tape, makes ''allegations that directly contradicts sworn testimony ... directly contradicts police statements he'd given previously, directly contradicts public statements and absolutely contradicts everything his family knows.''
Sandusky's arrest in November triggered a scandal at Penn State that led to the ouster of Hall of Fame coach Joe Paterno and the university's president.
The case has shone a national spotlight on the issue of sexual abuse against children. A spokeswoman for the Rape, Abuse & Incest National Network, which describes itself as the nation's largest anti-sexual violence organization said Tuesday there has been a 33 percent increase since the trial in the number of people who contacted the group's National Sexual Assault Online Hotline.