Journalism lost a special person the day Christopher Allen was murdered in South Sudan. The fact that very few journalists, let alone millions of others, know of his death in August 2017 is a tragedy behind a tragedy.

For Allen was a young reporter and photographer who, despite his inexperience, produced enough work to suggest he was going to make a special contribution to our trade. He wrote sensitively, almost poetically, from three conflict zones – Ukraine, Turkey and Sudan – while taking illuminating photographs and shooting videos.

So, how and why did Allen die? And why has his case received so little coverage?

Asking these basic questions brings into focus the increased risk of modern war reporting. Too often now, with big news organisations having left the field, it is freelancers who report from the frontlines. Yet, should they die, there is less of a media storm about their deaths than is usually the case for staffers.

Less media noise means less pressure on the relevant authorities to act. Consequently, there are too few proper investigations into journalists killed in the line of duty. It is becoming clear that over the past few years, there has been a growing acceptance that reporters and photographers, whether staff or freelancers, can be killed with impunity when covering conflicts. Allen’s case is therefore emblematic of the current situation.

Ever since he was killed, his parents, relatives and friends have been seeking an investigation into his death but have been thwarted by a mixture of official apathy in Britain, bureaucratic inertia in the United States and bloody-mindedness in South Sudan.

Allen, who held British and American nationality, was 26 when he died in South Sudan’s civil war. He was embedded with a group of rebels belonging to the Sudan People’s Liberation Movement-in-Opposition when they launched an attack on the government-held town of Kaya, near the border between the Democratic Republic of the Congo and Uganda.

According to initial reports, he was the victim of crossfire. This version of events was soon discounted because he was shot five times by government soldiers in the apparent belief that he was a “white rebel”. Could they have mistaken his camera for a weapon? It would seem highly unlikely and the Associated Press journalist Sam Mednick later interviewed soldiers who admitted they knew Allen was carrying a camera and shot him all the same. In other words, he was targeted as a journalist.

What happened immediately afterwards also calls into question the motive behind his shooting. Pictures taken of his clothed body were followed by images of him stripped naked as a form of humiliation, which were then posted on social media. These were taken down after the intervention of US diplomats.

South Sudan has refused all calls to hold an investigation. And a chance for Britain to hold an inquest into Allen’s death was missed when his body arrived at Heathrow en route to the US. That oversight is surely one of the consequences of there being too little publicity about the killing by British media.

As for the US, Allen’s family called for an investigation by the FBI because his suspected targeting as a journalist would amount to a war crime. So far, nothing has come of it, nor of attempts to persuade the United Nations to get involved.

But his parents, Joyce Krajian and John Allen, who live in the US, are fighting on. In a joint email to me, they said: “We must find justice for Christopher’s tragically short but well-lived life, thereby ensuring a safer world for journalists who report from conflict zones in the future.”

Allen’s London-based film-maker cousin, Jeremy Bliss, is also pressing for action. In a moving piece for the Columbia Journalism Review last month, he wrote: “At a time when journalism is more dangerous than ever, impunity only fuels threats against reporters such as Christopher.”

The case has been taken up by the global press freedom organisation, Reporters Without Borders, whose UK director, Rebecca Vincent, said: “The failure of the US and UK governments and the UN to act meaningfully for the better part of two years is nothing short of shameful, and we call on them to remedy this inaction now. When we campaign for justice for Christopher, we are also campaigning for the protection of journalists everywhere, and to ensure that our own governments never again allow this to happen when journalists are targeted abroad.”

A London law firm, Doughty Street Chambers, has also offered support to the Allen family. One of its barristers, Caoilfhionn Gallagher, points out that there is probable cause to suspect Allen suffered from a double war crime. The first, his killing for being a journalist, was compounded by the second: the outrage on his personal dignity by subjecting his body to humiliating and degrading treatment.

She said: “A journalist, whether embedded with an armed group or not, falls within the definition of a civilian and is entitled to protection. Journalists who bear witness to armed conflict are both exercising their own fundamental rights to freedom of expression, and performing a public service.”

Allen was determined to be a witness to conflict. In explaining his motivation for covering conflict, he said: “It is better to be on the frontlines of history rather than in a library studying it.” To that end, in 2014, Allen went to eastern Ukraine and came across the debris of Malaysia Airlines flight MH17, which was shot down by pro-Russia separatists and cost the lives of all 298 people onboard. His video and report, which reveal a talent for description, were published by the Daily Telegraph, giving him his first newspaper byline.

Later articles for American outlets showed an increasing development of his writing and photography skills. After a lengthy stay in Ukraine, he went to Turkey, where he was embedded with Kurdish militia, before he made his way to Africa and South Sudan.

His mother said: “Christopher had a desire to bring to light untold stories from uncovered and under-covered regions of the world, to show the plight of their peoples. He dedicated himself to covering what he felt were invisible wars.”

But Allen’s death should not be invisible. To let it pass without a rigorous investigation is to sanction the impunity of the killing of journalists.