"Well, there's no point in trying to draw conclusions just yet, we've got no evidence indicating who or what might be responsible for all this right now." Unless Kaiba saw something he missed? But yes, better to keep their minds clear and open so they can examine any future clues without bias.

He understands how frustrating it can be to not have any information on something so important -- he's a scientist, after all, solving mysteries is kind of his job. Just the mysteries of nature rather than the mysteries of man, in his case.

He is indeed just using an idiom, because, well... he honestly doesn't think about money that much. He's got enough to do his research, and to keep himself and his loved ones comfortable, and that's really all he needs.