Well a: he could work with LE if he felt this was some strong moral point, and b: LE saying that is definitely lying. There are other services, and there's now more solid ways (e.g. Monero) to hide cryptocurrency. So it's super unlikely it was just his service providing a totally unique thing and without bitmixer.io oh no criminals would just give up and return their sex slaves.

What about people writing secure messaging services? "This terrorist attack would have been prevented if it wasn't for your encryption!"