The family of a Scots journalist brutally murdered in a war zone are demanding that Tony Blair helps them get justice – 30 years after his death.

Malcolm Rennie, 29, was shot, stabbed and his body burned along with four other journalists covering the Indonesian invasion of East Timor in 1975. But Foreign Office officials won't call it murder – and nobody has ever been arrested for the crime.

Malcolm and Brian Peters, from Bristol, were working for Australian TV channels 7 and 9, with colleagues Gary Cunningham, Greg Shackleton and Tony Stewart. On October 16, 1975, Indonesian troops, disguised as East Timorese rebels swept into the village of Balibo.

The reporters had written "Australia" on their house, thinking the Indonesians would respect them as journalists. Instead they were brutally killed – but even today officials claim they were just caught in crossfire between rebels.

Last night Malcolm's cousin, Margaret Wilson, told how his family are still fighting for justice. And they want Prime Minister Blair and the Scottish Executive to put pressure on the Indonesian Government to punish Malcolm's killers.

Margaret, 59, said: "It's a shame that Malcolm's dad died without seeing any progress. Malcolm's mum died last year at 85. She went 29 years without seeing any progress. Nobody except us seems to want to know the truth. But we know it was murder and we have a pretty good idea of who did it."

The leaders of the Indonesian troops during the invasion have evaded the time limit for murder charges – but not for war crimes. But campaigners say it will take international pressure to get action.

So far, the Australian and British Governments have publicly accepted that the reporters died in crossfire between warring East Timorese forces.

But after 1994 it emerged that the Australians knew the journalists were in danger. And papers have revealed that British officials tried to persuade the Australians not to raise the British deaths with the Indonesians.

Files have been destroyed as "standard practice" and even photographs of the staged funeral were withheld until 1995 on "compassionate grounds".

After the United Nations took over in East Timor they started an investigation in 2000, treating the deaths as murder. But the UN Prosecutor General refused to issue arrest warrants for retired Indonesian cabinet minister and general Mohammed Yunus Yosfiah, Christoforus da Silva and an East Timorese, Domingos Bere.

Leading campaigner Hugh Dowson said: "Thirty years on, Scots should demand their Government help to put an end to a cover-up that allows Malcolm's killers to go on killing – and to go on laughing at the UN's efforts to bring them to justice."

Now the campaigners hope an inquest into the death of Brian Peters in Australia in December will return a murder verdict, allowing relatives to put pressure on officials in Britain to act.