There's been loads of foreshadowing in this manga, and they haven't expanded on it so far. It will probably happen soon tho, with how the manga is currently progressing.
A possibility is that there's way more depth in Ao's character than we think, and his involvement in all of this. After all, his sister was a target. There's also the fact he wasn't born in Japan, which probably connects somewhere, otherwise it wouldn't have been mentioned.
There's also this weird reaction when coming face to face with Peter infront of his house.
Kind of a weird response given that he just came out of his house. Did he know Peter before this point? I think peter did end up helping Ao, as he always said he is happy when Nezumi is happy, which she would be with Ao:
Also why is he holding a head here? Whose is it? Is this what he used to fake Ao's death? Pretty sure he's holding a wig here. He has hair in the previous panel, and no hair when he's holding it. Let's not forget the doctor lived right next to them, and he called Ao pants-kun, which means he knew him too:
There's a lot of other unexplainable pages, and they will probably tie all of this together at some point so it will make sense.