There's an answer. Mulroney got the payoffs in cash in hotel rooms... in the United States. The US has laws about handling amounts of cash over $10,000. You can't cross the border with it or put it in a bank account without paperwork. Mulroney must have violated some of those laws.
Canada was too gormless to prosecute Conrad Black, and now we're apparently too gormless to prosecute Brian Mulroney. Perhaps the US can step in again?
* We want our $2M back