wetaugust, I was just thinking about the Stephen Waldorf case. I lived in Earls Court at the time and I remember one of the local 'rent boys' running up to us and saying, "Don't go up there! The police are shooting people!!!"
As for this case, the guy had form and was known as an extremeley violent individual. Police officers are not superhuman. If they thought he had a gun in his hand, and they were scared, I am not surprised they shot him.
As others have said: Life by the Sword, Die by the Sword.