While there's anecdotal evidence (as seen in reports from locals at the scene ) that *some* of the rioters were locals, there's no way of knowing how many actually were.
I've been following this all pretty closely from day 1.. and what I notice is, the media, the police and the public are hugely *and for the most part, wrongly* conflating the "protestors" with the "rioters".
Fact is, the protest and the riot and two separate, if in places overlapping events.
While a mostly peaceful protest lapsed into violence on the Saturday night (some of this provoked by criminal gangs who can be seen clearly on film attacking sports fans at a bar, and using the chaos to rob people - I'll put a link to this when I can find it, it's very revealing) things didn't go truly pear-shaped until Monday afternoon.
Monday afternoon being the time scheduled for a "purge event" that was advertised far and wide on social media, had a planned route for rioters to follow and encouraged people to attack police. It totally and very obviously hijacked the protest.
Clearly, this was a completely separate agenda to that of the protest. Organised by persons unknown.
This was NOT an organic development of the protest. It was planned, it was intrusive, and it had nothing to do with Freddy Gray, or justice for anyone. And the rioters could have come from anywhere, as the riot was advertised days before it happened.