"Yeah," he confirmed, "Although it would be nice to have someone a little bigger around, in case something goes wrong."

Because Roddy certainly wasn't going to be nosing around in his human form when they already suspected him of murder. He didn't want them thinking he was trying to hide the evidence, or plant new evidence. Sirius being there, whether in dog or human form, would make things a heck of a lot easier, though, and he'd rather not investigate a possible murderer alone.

"And if nothing else, I'm pretty easy to smuggle around in my other form. You said yourself a rat can be good at sneaking."