I think we are witnessing two different series of events.
1. Bruno made a plead, just before he died.
2. His account was sold/hacked.
The way I see it, the hacker/buyer
waited for the funds to be moved by Bruno's family, to start posting using Bruno's Cage account.
If that hypothesis is correct, then the imposter will never be able to sign anything from the plead donation address.
It's strange, that the person who accessed his phone/ computer/ laptop somehow managed to know Bitcointalk. Could be an acquaintance/ friend of him.
Butt hurt enemy?