Looks like some idiot left their suitcase lying around and wondered off: http://www.stratford-herald.com/55810-controlled-explosion-carried-out-in-stratford.html

The trouble is, as others keep telling us, terrorists only need to be lucky the once. And of course, the fear that that creates is just what they play on.

Yes, that's the case nowadays. It's good to see the police erring on the side of caution, and it'll teach the owner of the suitcase not to leave their luggage lying around!