The jury has returned its verdict in the final trial of the 21 young people charged with murder at London's Victoria station in March 2010. The prosecution had no clear evidence of who struck the fatal blows, so they relied on "joint enterprise", the controversial legal doctrine which can make a group liable for a crime committed by one of its members. It works like this: when A, B and C participate together in one crime, during which A commits a second crime which B and C have foreseen he might intentionally commit, joint enterprise makes them all guilty of it.

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