There was a crucial week at the end of November 2011:
On November 25th, Newsnight editor Peter Rippon sent an email saying he was still very enthusiastic about the investigation.
On 29th November, the BBC Christmas schedules were published.
On 30th November, Rippon sent another email to his team saying he'd had a change of heart and that he was no longer sure the story was strong enough to run.
On 1st December he pulled all editing on the programme entirely, effectively ending the project.
The question is: Did he feel he had to pull the programme because of the tribute programmes? Or was it because of the new information he was given the previous day by the reporter which made him question the project editorially?
The BBC said this will be examined in the investigation run by former head of Sky News Nick Pollard.
Amid the fallout from the Jimmy Savile scandal the BBC is investigating nine allegations of sexual harassment among staff and contributors.
BBC boss George Entwistle has spent almost two hours taking questions from MPs about the corporation's handling of the Savile scandal.
Ex-BBC boss Mark Thompson has told ITV News he will help with any inquiry into the corporation and its handling of the Savile allegations.