...He is responsible for his actions which resulted in his death...
The question remains, if the police belived that he were a suicide bomber, why they let him on a crowded place like an underground station, they could challenge him or wound him on more quiet streets from that house to the underground...
These types of things rarely go 100% the way the police plan. He ignored warnings and continued to run, jumped a barricade and ran onto the train. If the police had done as you suggest and he had a bomb and it had gone off, they would have been criticized for allowing him in a residential neighborhood. It's a damned if you do or damned if you don't scenario for them. As tragic as the situation is, I don't think that they bear 100% responsibility for this man's actions.