Members of one of the Philippines’ most powerful political clans have been found guilty of a massacre that left 57 people dead in the country’s worst case of election violence.

At a special court in Taguig City, five members of the Ampatuan family, which governed the southern province of Maguindanao for decades, were sentenced to life imprisonment for the killings.

The massacre was found to have been overseen by Andal Ampatuan Jr, a former town mayor and son of the former governor Andal Sr.

The verdict, which follows a 10-year battle for justice, was welcomed by families but was described a partial victory. Some members of the Ampatuan family were acquitted. A further 80 suspects remain at large.

The group were accused of ambushing and killing members of the rival Mangudadatu family, who had been on the way to file election candidacy papers for Esmael Mangudadatu.

Mangudadatu, who planned to run as governor of Maguindanao, said that he had received death threats from the Ampatuans. He sent his wife and supporters to file his candidacy, in the belief that they would not be attacked.

Their election convoy was ambushed and shot by 100 gunmen. Among those who were killed were 32 journalists and media workers, who were covering the filing of Mangudadatu’s candidacy papers.

It was one of the world’s biggest single attacks on journalists.

Victims’ bodies were buried with their vehicles in a pit dug by an excavator. At the time of the massacre, the then justice minister, Agnes Devanadera, said the bodies of many of the 20-plus female victims had been sexually mutilated.

Jhan Chiene Maravilla, whose father Bart Maravilla, a radio reporter in the convoy, was killed during the attack, said she welcomed the sentencing. Families, however, remain afraid for their lives because many people were acquitted, she said.

“Some of them are now free. What happens to our families? They might try to to retaliate. We can’t be sure. They killed 58 people. They can kill us one by one. We know their character. They really need to stay in jail,” added Maravilla.

Nonoy Espina, the chairman of the National Union of Journalists of the Philippines, described the verdict as a partial victory. A further 80 suspects remain at large.

The Ampatuans have denied the charges against them.

Throughout the case, which has dragged on through the courts for almost a decade and involved roughly 100 defendants, victims’ families and media groups have reported harassment and threats.

At least three witnesses who testified in the case have been killed over the years, Nena Santos, a lawyer for Mangudadatu and families of several other victims told Associated Press. Santos said she had been threatened with death multiple times and offered a vast sums to withdraw from the case.

Antonio La Viña, a professor at the University of the Philippines College of Law, said the battle for justice was not over. “The enabling conditions for the massacre – warlordism and political dynasties – still is exist in many parts of the Philippines. The Ampatuan Massacre was state sanctioned, state violence in the extreme,” he said.

The sentencing did, however, offer hope, she added, by sending “a strong signal that impunity is not forever”.

“It might take 10 years but justice will catch up,” La Viña said. “These were crimes against humanity like the killings in the war against illegal drugs. Those who are responsible for the latter should know they will not elude justice.”

The case has been seen as a test of the Philippine courts, which are notoriously sluggish, underfunded and vulnerable pressure from elites.

Phil Robertson, Human Rights Watch’s deputy Asia director, described the verdict as momentous, adding that it should “spur further political and judicial reforms to ultimately end the impunity that has plagued the country for far too long”.