Whenever you get an organisation in charge of others, through legal means, you will always have those who greatly abuse their position, and I don't think anyone can be an exception...
However, to play devil's advocate, sometimes, when an officer is in the front line, and has to rely on what they see and hear, they only have a split second to make a decision, and to act, to the safety of others around them. I am not necessarily defending the shooting of the Brazilian in the UK, but people in the front line are under enormous pressure to do the right thing and to abide by the law. Sometimes, the two do not seem to always go hand in hand. They have to think with seconds to spare, because they simply cannot predict the outcome... so it can't be easy.
