Police in Rome say seven men were injured. Five were British, one Californian and one Bangladeshi.
A group of about 40 or 50 people in motorcycle helmets or with their faces covered were armed and attacked the group of English football fans drinking in Campo de Fiori square. The more seriously injured seems to be the Briton born in 1987. The American was born in 1982.
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The letter calls for an end to harassment, abuse, and impunity in a world "ripe for change".
Police say that anyone who sees Whitehouse should not approach him, but instead call them on 999 and quote incident 23 of 18 February.