Don't blame the police - blame Hussein Osman
It was Osman who the day before tried to blow up a train full of passengers at Shepherd’s Bush, Osman was linked to the block of flats in Stockwell where Mr de Menezes lived, and it was Osman whom the police thought they were following. Had Osman not existed, or else been content with allowing his fellow citizens to exist in peace, Jean Charles de Menezes would still be alive.
The people responsible for terrorism and it's consequences are not the police or government but the terrorists.