There are fears over Olympic security after a known terror suspect entered the Olympic Park five times in a single day.
The British-born jihadist was arrested after breaching an order banning him from the area.
It's raised questions over security just days before the Games are due to begin.
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While #SevenSeven has been trending for much of the day, so too has the #WalkTogether campaign.
Police want to find four boys seen on CCTV around the time of the attack.
Georgina Ferguson was on a carriage behind the one that was bombed. This is her very personal story of 7/7.