You are almost right. All the terrorists inside the building were killed, but in the evacuation some of the terrorists tried to pose as hostages and escape down the stairways. They were pointed out by the other hostages and killed by the SAS...except for one. After the evacuation was complete and the hostages were being counted in the grounds, one more terrorist was identified. He (name of Fowzi Nejad) is currently in prison serving a 25 year term. Which means he is probably due for release about now....
Leave one alive to tell the others how bad it was.....