I'd be very wary of presuming the brother's guilt on the basis that he came across a bit fishy in selective footage from a documentary. Isn't that precisely the kind of behavioural prejudice that led to Avery being arrest for the '85 rape in the first place? Less so in fact, as he'd actually rammed a woman off the road and threatened her with a gun, as opposed to "seemed single minded and a bit 'off' in interviews following his sisters death..."
If there's anything I've even less faith in than the US Justice system, it's the internet justice system. From reddit wrongly identifying an innocent missing person as a terrorist during the Boston bombings, to half a million people petitioning for a Presidential Pardon for Avery last week, despite the fact the President can't pardon state prisoners, it's pretty obvious the well meaning online crusaders are just as liable to be ignorant and reactionary as the police are.