Omg
Did he though?
Maybe by accident but I think that’s what the father is implying
Knowing how these stories usually go with misunderstandings, I wouln't jump into conclusion so soon.
I think he wanted to get them into some type of accident and then it was way worse than he had thought. So he did kill them but it wasn't all his intention.
So he killed his adoptive parents （￣へ￣）