Because he had once worked closely with Orochimaru, Danzo held a great deal of incriminating material, and he knew all about even some of the more secretive laboratories and illicit materials.
Thus, Danzo planned to make Orochimaru his first point of attack. He had no intention of directly implicating Nawaki, because he knew full well that Nawaki's reputation throughout Konoha was simply too good. Without direct evidence, no one would suspect him. It might even alert the enemy and allow them to turn the tables on him.
Having learned from his previous failures, Danzo had grown increasingly cautious in his methods. He knew he had only one chance this time, and that failure would bring dire consequences. Therefore, he did not intend to use rumors to broaden the matter's influence. He did not even plan for himself or Root to become directly involved.
He intended to use the Uchiha Clan to light the fuse for the entire plan, having them reveal Orochimaru's secret human experimentation to Hiruzen.
The reason Danzo did not personally hand the evidence to Hiruzen Sarutobi was, first, that he and Orochimaru were still allies on the surface. If he directly sold out his partner, no one would cooperate with him in the future. Second, if he handled this himself, it would easily arouse Hiruzen's suspicion and expose his true purpose!
The Uchiha Clan controlled Konoha's Military Police Force, and they had always maintained a fairly good relationship with Nawaki. Having them file the report was entirely within their duties and would not invite suspicion.
And that was precisely why Danzo had chosen to cooperate with the Uchiha Clan.
Before long, the Uchiha Clan and Danzo each began making their moves in secret. Meanwhile, Nawaki and Orochimaru continued to spend every day in the laboratory, seemingly unaware