Volunteers are not collateral damage. They are not acceptable targets when a ceasefire ends. Ceasefire or no, the rules of international humanitarian law still apply. Safe access must mean safe access. Guarantees given by fighting parties must be honoured. This recent attack has horrified people across the world. It has also denied 78,000 people of much-needed aid. These attacks cannot and must not continue. We call for all aid workers to be respected and protected. This, sadly, may not be the first time aid workers have been attacked. But it should be - it must be - the last.