Louis Freeh said he expects his inquiry to go back as far as 1975, which is a longer period that a grand jury report issued earlier this month.
Freeh said his goal was to conduct a comprehensive, fair and quick review. His team of former FBI agents, federal prosecutors and others has already begun the process of reading the grand jury report and looking at records.
"We will immediately report any evidence of criminality to law enforcement authorities," said Freeh, who has no direct connection to Penn State.
In the meantime, a psychologist treating one of the alleged victims broke his silence Monday in an interview with "Good Morning America." Michael Gillum has been counseling the young man known solely as Victim 1.
Sandusky's attorney has already said he will go after the credibility of the young man following allegations he changed his story.
But his psychologist says victims of abuse often take time to reveal the details of what happened.
"The level of humiliation, the level of insight into how deviant what's occurred is, means that they're not going to reveal that until they really feel comfortable," Gillum said. "And that may take months, that might take a year or two."
The victim's mother told ABC News that her son left his high school after being bullied severely. Students found out he triggered the child sexual abuse investigation.
An attorney for former head coach Joe Paterno said the coach condemns harassment or bullying of any kind.
The Associated Press contributed to this report.