He makes a good point, which is always dragged out whenever people discuss capital punishment. His point is that there has been historic miscarriages of justice in incidence of poor work by detectives (incorrect DNA testing, circumstantial, unreliable witnesses etc.) Not sure it's applicable in the case of someone committing a crime in plain sight of 40+ people.
I'm no in favour of it, just not sure the above is relevant to this case.