There are two aspects in answer to his question.
First of all, it is part of the mandate; allow me to refer to it:
[...] in particular, the handling of allegations by the present and past governments including the circulation of relevant correspondence in the Privy Council Office and Prime Minister's Office [...] to examine whether there were violations of ethical and code of conduct standards by any office holder [...]
Secondly, Mr. Schreiber mentioned on several occasions that he asked Mr. Mulroney to intervene on his behalf with the Harper government. Therefore, it is helpful if not necessary for the committee to know if Mr. Mulroney had the necessary contacts and influence in the Harper government, as Mr. Schreiber stated.