Who was 'Deep Throat' for Grewal's election expense story?

There is a very good exchange taking place over at Bound for Gravity in there comments, which in many ways is a model of how discussions in blogs should go. There are a variety of opinions being made from a variety of stand-points, mostly done respectfully and intelligently. Let's see more of that!

One point made there by one of the Tories, Vitor Marciano (who is a national councillor in the Conservative party) is this:

There is something very strange about this report: Elections Canada has its own investigative arm which -if the facts reported by CBC are correct- would have jurisdiction on this matter. The RCMP would normally only be called in after an Elections Canada investigation and determination. Something smells about this report!

The implicit question is what is the source of the CBC story. It is not impossible, of course, that the CBC dug all this up themselves: one of the contributors, having failed to get satisfaction from Grewal's constituency office leaked their story to the press at the height the Grewal scandal and this is patient slogging since. Against that idea, I think, is the fact that they found five people with similar complaints. They would have surely have reported the story at three.

The other possibility is that the source is in the RCMP (or Elections Canada), who leaked to the CBC reporter the names of those who had made complaints. Although this happens all the time, this would, I think we'll all agree, be inappropriate.

The third possibility--and the one that I think is likeliest--is that this is coming from within Grewal's own office in Surrey. Why suppose it might be someone there? First, opportunity. Grewal's office will know who the contributors are (because they will have been trying to get their receipt for months now), and they know whether there is an RCMP investigation (they will have been interviewed). Second, motive. It is pretty obvious that Grewal has no chance of re-election in that riding; Harper stuck with Grewal through the worst of the tapes fiasco, and (having survived that) it must look like there is no possibility to rid themselves of Grewal. But wait. There are these problems with the contributions.

So, who is Deep Throat? The CBC report includes this detail:

Grewal said in a telephone interview that he turned over all contributions to his riding association, but his own official agent John Keith contradicted that, saying he never received the cheques in question, which is why he never reported them to Elections Canada or issued receipts.

It strikes me that Mr. Keith seems to have answered this question much more specifically than we would expect him to: he refers to the specific cheques that he did not receive. Why? Presumably he's been wrestling with this particular nest of problems for a while. But it also seems that he has no great desire to defend Grewal, and perhaps justifiably so. If Mr. Keith has been dragged through an Elections Canada audit, and now has been interviewed by the RCMP, his enthusiasm for Grewal may be substantially diminished. Is it possible that he saw his chance to rid his constituency association of its greatest liability?

[Edited for clarity]

Update. Look also at this clip from a story in the Vancouver Province :

Grewal told CBC he gave his riding association all contributions, but the MP's official agent, John Keith, said he never got them.

The party told CBC two of the cheques went to a supplier for campaign expenses.

This seems to imply not only were contributions taken and not chanelled properly through party machinery, but that expenses were, too. But note that it is the party that is the source for the fact that campaign expenses were paid with these cheques. It is difficult to see how that piece of information could be coming from anywhere but within Grewal's office.