11 years ago, journalist Anton Hammerl became the story when he was killed in Libya by pro-Gaddafi forces. And now, a decade later, his family wants to ensure his story is told.

In early 2011, Anton Hammerl, an experienced, award-winning photojournalist and photographer, travelled from his home in London to Libya to cover the civil war, part of a wave of pro-democracy uprisings known as the Arab Spring. He entered Libya at a time when Muammar Gaddafi's forces were suspected of serious violations of international humanitarian law, including war crimes and crimes against humanity, to bring accurate accounts of what was truly happening.

On April 5 2011, days after arriving in Libya, Hammerl and three other journalists –US journalists James Foley and Clare Gillis and Spanish photojournalist Manu Brabo – came under fire while covering the conflict from forces loyal to the nation's ruler, Gaddafi. Anton Hammerl was fatally shot. Foley later described what happened: seeing two heavily armed Gaddafi vehicles coming over the rise of the hill, shooting heavy AK47 fire, and the four journalists pressing themselves as close as they could to the ground because they immediately knew they were in danger of their lives; the realisation that this was not crossfire aimed at the rebels – the journalists were being shot at directly.

Hammerl's case is not only deeply troubling in itself, but is emblematic of the ongoing impunity concerning war crimes and crimes against humanity by government forces in Libya at that time. It is also a stark reminder of the importance of the work of photographers, who play a vital role in bearing witness to armed conflict, taking risks to perform a key public service.

Now, on 19 May, Hammerl's family is calling on the international community to fill the investigative void and take the action Libya has failed to take since April 5 2011. The date of 19 May marks the day on which Hammerl's family were told he had been murdered by Gaddaffi militia, after previoulsy being led to think he was alive for 44 tortuous days.