I tried pinning Regulus down on those matters myself more than once, and you're quite right that his history was more with witches than otherwise.

I will speak with Mafalda about the matter, but you understand it's the traitor's network that is of on-going concern to the department. Frankly, I've a feeling she'll suggest a private investigation into the questions regarding Regulus's past. As you know, the official investigation into his whereabouts during those years was quashed early on, and while it's my understanding that there has been no actual instruction from Buckingham to direct efforts away from that aspect of the current case, there has also not been any encouragement.