Here’s how I think the whole thing played out.
Barney goes to K9 boot camp with a bunch of other dogs who are sent off to chase down drug smugglers and battle terrorism while he ends up guarding teddy bears in an obscure London museum. So naturally, one day he snaps.
Barney ripped the head off a brown stuffed bear once owned by the young [Elvis] Presley during the attack, leaving fluffy stuffing and bits of bears’ limbs and heads on the museum floor.
update – After finding this photo of Barney, I’m ready to adopt him. We’re already pretty good at handling charges that are inclined toward an occasional messy public outburst.