If this incident began with a planned approach by the police, on the assumption that they might be facing someone violent and armed, one of the first questions

If this incident began with a planned approach by the police, on the assumption that they might be facing someone violent and armed, one of the first questions should surely be why any officers outside the building were so exposed that they were concerned about being suddenly shot by the suspect. Do these officers not arrive equipped with body armour, shields, armoured vehicles and the like in a situation like this?