And, making a statement today after a video of Mr Haines’s death seemed to once again feature a man with a British accent who could be the extremist dubbed ‘Jihadi John’, Mr Cameron said Britain would continue its efforts to track down and bring to justice the people responsible for the killings ‘no matter how long it takes’.
Mr Cameron said that the men responsible for the deaths of Mr Haines and others ‘are not Muslims – they are monsters’, and set out a five-point plan of how the UK would co-operate with the international community to end the extremist threat.
‘David has been murdered in the most callous and brutal way imaginable by an organisation which is the embodiment of evil. We will hunt down those responsible and bring them to justice no matter how long it takes.
‘David Haines was an aid worker. He went into harm’s way not to harm people but to help his fellow human beings in the hour of their direst need from the Balkans to the Middle East.
‘His family spoke of the joy he felt when he learned he’d got his job in Syria. His selflessness, his decency, his burning desire to help others has cost him his life.
‘But the whole country, like his grieving family, can be incredibly proud of what he did, and what he stood for in his humanitarian mission.
‘David Haines was a British hero. The fact that an aid worker was taken, held and brutally murdered at the hands of Isil sums up what this organisation stands for.
‘They are killing and slaughtering thousands of people – Muslims, Christians, minorities across Iraq and Syria.
‘They boast of their brutality. They claim to do this in the name of Islam. That is nonsense. Islam is a religion of peace. They are not Muslims – they are monsters.
‘They make no secret of their desire to do as much harm – not just in the Middle East – but to any countries or peoples who seek to stand in their way, or dare to stand for values that they disagree with”.