This is the 21st Century people. Things are different now. The rioters will be bragging on Faceb***, Tw****r, webpages, forums, emails, in videos, and in any amount of electronic methods.
Each one is traceable, and the anarchists and thieves are too dumb to realise the massive electronic trail they'll be leaving.
The Police just need the manpower to track down all the electronic trails, and then go and find and arrest the troublemakers. Simple really. They won't be able to help themselves, bragging about all the stuff they've pinched.
The bigger problem is that real punishment won't be in line with what they deserve. They deserve to be sent out cracking rocks with a sledgehammer at 50p an hour, until the authorities have recovered the full cost of the damage caused.
However, that won't happen. The jails are already full, and they'll be sent home with a sharp-telling off, and a community order... and the ordinary folks will be left to pick up the tab... via higher rates, taxes, and insurance premiums.