The BBC's foreign affairs editor John Simpson returns to Kurdistan nearly 25 years after the world's worst-ever chemical weapons attack on civilians. He hears from the survivors of the attack, launched by Saddam Hussein's regime against the citizens of Halabja at the tail-end of the Iran-Iraq war. It is thought to have claimed more than 5000 lives, most of the victims killed within minutes, as a lethal cocktail of nerve agents and mustard gas spread through the town. With the fall of Saddam Hussein's regime, and his trial and execution in 2006, much has changed in this region of Iraq, but for many citizens of Halabja there remains a quest for justice and closure. A British forensics company now believes it can help by identifying the precise chemicals used and the European companies suspected of supplying them.