The broadcaster said it obtained the complete file of an early investigation of Sandusky carried out by Penn State University police 12 years before he was charged with more than 50 counts of child sex abuse.
Among the revelations in the file was a report from State College, Pa., psychologist Alycia Chambers -- the therapist for one of Sandusky's alleged victims -- who warned then the coach displayed a "likely pedophile's pattern" in his conduct with the boy.
The file indicates the probe was launched after the alleged victim's mother claimed the boy told her Sandusky "bear hugged" and kissed him while they were naked together in a shower.
But the investigation was wrapped up after "it could not be determined that a sexual assault occurred."
"There was very little doubt in my mind [Sandusky] … was a male predator, someone that was in the process of grooming a young man for abuse," Chambers told NBC News. "I thought … my report was strong enough to suggest that this was somebody who should be watched."