BELLEFONTE — An investigator who arrested Jerry Sandusky said the case started slowly but grew.

The probe began with a report of abuse in Clinton County, then moved to an anonymous email leading investigators to Mike McQueary, to paging through Sandusky's autobiography for clues.

"It was a daunting task to try to get other victims to come forward," said Anthony Sassano Thursday.

A narcotics agent with the state Attorney General's Office, Sassano testified for the prosecution in the Sandusky child sex abuse case Thursday.

He said the investigation began in December 2008 after one of the alleged victims contacted a school guidance counselor and Children and Youth Services got involved. The investigation proceeded to a grand jury about six months later.

Sassano said Centre County District Attorney Stacy Parks Miller received an anonymous email tip to contact McQueary, who was then Penn State's wide receivers coach.

McQueary testified Tuesday that he walked in on Sandusky naked in what appeared to be a sexual position with the boy in 2001, when McQueary was a graduate assistant.

He said he told university officials and Joe Paterno what he had seen.

Sassano testified about what investigators found in about 20 boxes of paperwork Sandusky had left in athletic facilities on campus. Among the papers found in the boxes were photographs of alleged victims and roster lists of Second Mile camp attendees, including some alleged victims whose names were marked with asterisks.

Also included were daily schedules and bus passenger lists for a trip to the 1999 Outback Bowl with the name of alleged victim No. 4.

The prosecution showed the jury dozens of documents and photos obtained through search warrants that also referenced some of the alleged victims who have testified against Sandusky this week.

Sassano said investigators used Sandusky's autobiography to find references to names and photos, and tried to track down more leads once they identified people in the book.

Sassano also revealed how investigators homed in on the date change of the shower incident that McQueary testified about. Sassano said he bought old issues of TV Guide to find the Friday night that the movie "Rudy" aired — it was at 8:05 p.m. Feb. 9, 2001, on cable network TBS.

He also confirmed the date with Jonathan Dranov, a friend of Mike McQueary's father, who was called to the McQueary residence that night.

Sassano said Penn State did not respond quickly to a subpoena seeking information about university employees who might have been in the athletic facilities during off-hours.

"Penn State, to be quite frank, was not very quick in getting us our information," Sassano said.

At that stage of the investigation, the university was under its previous administration.

More recently, university officials have said they are fully cooperating with the attorney general's investigation and turning over relevant documents as soon as they come across them.

A university spokesman said that in deference to the legal process, the university won't comment on specifics of the case.

Anne Danahy can be reached at 231-4648. Follow her on Twitter @AnneDanahy

Mike Dawson can be reached at 231-4616. Follow him on Twitter @MikeDawsonCDT