Matt Sandusky, in a 29-minute taped interview with police on the eve of Jerry Sandusky's trial on child sex abuse charges, describes how he was allegedly molested by his foster father from age 8 to 15, NBC's Today show reports.

Sandusky, a former Penn State assistant football coach, was convicted last week of 45 counts of child abuse and is in prison awaiting sentencing.

Matt Sandusky, who earlier denied to a grand jury encountering any inappropriate behavior from his foster father, approached police a week before the conviction and was being prepared by prosecutors as a "surprise witness" in rebuttal if Sandusky took the stand in his own defense, NBC News reports.

In excerpts from the taped broadcast on the Today show, the 33-year-old Matt describes how he would curl up in a fetal position and pretend to be asleep when Sandusky would come into his room at night, NBC's Michael Isikoff reports.

Recalling the testimony of other Sandusky victims, he says it was "like the showering, with the hugging, with the rubbing, with the just talking to me, the way he spoke."

At one point on the tape, Matt replies "yes" when a detective asks if the incidents included "rubbing along and against your genitals."

While being questioned by an investigator, he says Jerry Sandusky would blow raspberries on his stomach and touch his genitals, the Associated Press reports.

Asked if he recalled engaging in oral sex or being raped by the former Penn State coach, Matt Sandusky says "at this point I don't recall that."

Sandusky, NBC News reports, also says he ran away from home on one occasion and on another tried to commit suicide.

"I really know I wanted to die at that point in time," he says on the tape, obtained exclusively by NBC News.

NBC News quotes Sandusky defense lawyer Karl Rominger as saying his client was "very upset" when he learned that Matt was talking to police, prompting the 68-year-old Sandusky's decision not to take the stand in his own defense.

Rominger, however, challenges Matt Sandusky's portrayal of events. "Did we believe what Matt Sandusky said? Absolutely not."

NBC's Isikoff also reports that Sandusky, who was adopted by Jerry Sandusky and his wife, Dottie, at age 18, continues to undergo therapy and is only now recalling more details about his encounters with Sandusky.

Rominger, quoting from the tape, tells ABC News that at one point Matt Sandusky expresses concern that he could face perjury charges because his claims contradicted his earlier statements to the grand jury.