As his murder trial began in December 2009, Arvel Marshall made a desperate plea to his lawyer: Ask for surveillance videos of the Brooklyn street where he was accused of fatally shooting a 22-year-old man. Mr. Marshall’s lawyer made a halfhearted request for the footage. The prosecutor said initially that it did not exist, then that it was not accessible, and the judge moved the trial along. Mr. Marshall was convicted and sentenced to 25 years to life in prison. The video in question, captured from a nearby building, showed two men, neither of them Mr. Marshall, walking down a Crown Heights street toward where Moustapha Oumaria was sitting outside his home with three friends.

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Persons: Arvel Marshall, Marshall, Oumaria Locations: Brooklyn