He talked about how the case evolved from one accuser to 10 alleged victims and how an anonymous tip led them to Mike McQueary.
Anthony Sassano - the lead investigator - showed - what some would consider - bizarre letters that Jerry Sandusky allegedly wrote and addressed to one of his accusers.
Sassano testified one letter read in third person -"Jer became attached to (accuser) and always will be."
It also read "Jer may not be worthy, but he needs a best friend."
Sassano showed the letters on a projector screen.
Sandusky appeared to slightly smirk while the text was being read.
Sassano also showed photos of one of the accusers that were allegedly found at Sandusky's home and in a storage closet on the Penn State campus. Some showed him in a football uniform - some of him playing sports.
Sassano told the court an anonymous email to the Centre County District Attorney's office lead them to Mike McQueary who said he saw Sandusky assaulting a boy in the shower.
A lot of the witnesses and information Sassano uncovered - he said came from knocking on doors - identifying kids in second mile photos - and just asking around.
In fact - the testimony from the janitor - Sassano said is a result of tracking down the people who would be in the locker rooms during off hours.