One of the protesters, Chris Howson, told the Newham Recorder that arms fairs like this one were "fuelling the wars of tomorrow".
He said: "We are here to pray for peace because most people have no idea that they are selling weapons that can be used to kill women and children.”
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Omid Saidy, 20, was knifed to death after asking a drug dealer and another man to leave the area, police say.