What did 94 Conservative candidates know, and when did they know it?

Sixth Estate has a brilliant roundup post gathering together all 94 of the ridings where fraudulent or harassing phone calls have now been reported:

It’s become increasingly clear that there was not one effort to suppress votes during the 2011 election: there were several, some with robocalls, some with live callers, some with just plain idiots participating.

But there is one aspect of this scandal that hasn't yet received the attention it should have -- the cui bono question, who benefited?
The Conservative MPs who got elected due to these tactics -- or who lost but not for lack of trying -- need to be held to account.
Sixth Estate says later in a comment that

Given the scope of the operation, it’s almost inconceivable that local candidates would have been informed. In fact, whoever was responsible probably stayed away from sharing too much with individual candidates — less opportunity for leaks/objections that way.

Yes, that's true. But ultimately the individual candidates are responsible for EVERYTHING that was done in their ridings during a campaign.
The heart of the in-out scandal was how some Conservative candidates allowed their riding accounts to be used by the national campaign to launder national expenditures and get fraudulent reimbursements.  So its not as if local campaigns would not also be culpable in this scandal -- regardless of whose idea it was or where the phone call originated, local input would have been crucial to write those phoney redirection scripts.
When we hear during election campaigns about signs being defaced or removed, the media doesn't hesitate to phone up the offending campaign and go after the candidate for an explanation -- so why, in this scandal, have the MPs or Conservative candidates not been asked to explain what they knew and when?