There were quite a few people who had knowledge of the Sandusky investigation prior to Ganim's article. This includes more than ten who testified in front of the grand jury and would have been free to disclose their testimony and knowledge of the grand jury investigation to anyone. Those include:
In mid 2009:
Victim 1
Steven Turchetta
Joe Miller
In late 2010:
Mike McQueary
In early 2011:
Joe Paterno
Tim Curley
Gary Schultz
Katherine Genovese
Centre County CYS director
Ronald Schreffler
Former Centre County ADA in 1998, Karen Arnold
John McQueary
Jonathan Dranov
None of the above witnesses were prevented from disclosing their testimony or knowledge of the grand jury investigation. Anyone they might've spoken to would have had indirect knowledge of the grand jury investigation. Anyone that police had interviewed would have had knowledge of some sort of investigation.
There were rumors about the investigation among the CMHS football parents. These rumors would have started after Sandusky was banned from helping the football team in fall 2009. The parents allegedly knew accusations were made by Victim 1. A likely source of the rumor was the football coach Steven Turchetta who had testified to the GJ. (It might have slipped out innocently enough to his quarterback on the team, who's last name was also Turchetta.)
Police had also interviewed four CMHS students besides Victim 1 about Sandusky in January 2009.
There are reports (from a Towny) that Joe Miller told Paul Suhey about the investigation as early as 2009.
Matt Sandusky was interviewed by police in October 2009.
Lisa Powers testified at the July 2013 hearing for CSS that Jan Murphy, a Patriot News reporter, emailed Spanier in September 2010 asking if he was aware of a criminal investigation involving Sandusky.
The Moulton report indicates a Centre Daily Times reporter was seeking comment from Victim 1 on November 2, 2010.
Stacy Parks Miller received an anonymous tip about the Sandusky investigation and that McQueary might have knowledge on November 3, 2011. She forwarded the tip to Rossman.
Ganim has reported she was in contact with Victim 6 and/or his mother in January 2011. Her report referenced identifying other potential victims from Sandusky's book, Touched. Victim 7 was among those identified, and he had been interviewed by police in early February 2011, where he identified among other potential victims, Victims 4 and 5, also from pictures in Touched.
Ganim's article also cited the mother of B.K., the other boy interviewed by police in 1998, as a source.
Lisa Powers also testified that Al Horvath mentioned Tom Harmon had a reporter camped out his residence in February 2011 and was asking questions about an investigation of Sandusky.
Police interviewed various Penn State football coaches and athletic staff in mid February 2011.
Matt Sandusky's ex-wife was interviewed by police in March 2011, ten days before Ganim's article.
Here are supporting timeline events from the Moulton report: