Did everyone forget that last time they heard his "partner"'s voice (afaik his name was Nobuto) and thus realized he was connected to the syndicate, which is why they killed him.
@Metonym only if they find the box, which is dime a dozen. And flamable. And they have to give a shit in the first place.
Dude dead at home, fishy person. Propably overdosed. Case closed.