The question was benign: How did you know the defendant? But the answer from a witness — that she met Christian Bey when he moved in across the street after his release from prison — was enough to cause a mistrial. Bey, 34, was on trial in connection with the shooting death of off-duty Pittsburgh police Officer Calvin Hall in July 2019. Hall, 36, was shot on Monticello Street on July 14, 2019, following an argument with a group of people who lived there. Police said Hall had walked away when Bey, whose mother was among the people fighting with...