Andal Ampatuan Jr and several of his relations were on trial for the murder of political rivals and journalists.

A court in the Philippines on Thursday found members of the politically powerful Ampatuan family guilty in the murder of 58 people – including 32 journalists – in killings carried out 10 years ago on the southern island of Mindanao.

Three generations of the influential family were among 101 people on trial in a case seen as a crucial test of impunity in a country where provincial power is often decided by corruption, intimidation and violence.

The brazen attack was the country’s single worst case of election violence.

A Manila court on Thursday found Andal Ampatuan Jr, who had been planning to run for provincial governor at the time of the killings and four other relatives guilty of murder.

They were each sentenced to 30 years in jail without parole.

In an immediate reaction to what he described as a “momentous” verdict, Human Rights Watch Deputy Asia Director Phil Robertson welcomed the decision.

“Advocates should use this verdict to spur further political and judicial reforms to ultimately end the impunity that has plagued the country for far too long,” Robertson said in a statement.

“This verdict should prompt the country’s political leaders to finally act to end state support for ‘private armies’ and militias that promotes the political warlordism that gave rise to the Ampatuans.”

Justice ‘someday’

The group of 58 was going to file Esmael Mangudadatu’s candidacy papers to run against Ampatuan Jr whose family ruled over the province of Maguindanao with guns, violence and intimidation when they were ambushed by armed men.

Ampatuan Sr, then-governor, had been grooming his son as next in line to their political dynasty and feared Mangudadatu’s candidacy would disrupt his plans.

Mangudadatu had sent his wife and female relatives to file the papers taking along lawyers and journalists, for added protection, but it was not enough.

After being ambushed, the victims were moved to a hilltop and brutally murdered; their bodies dumped in a shallow grave.

The brutality of the attack outraged the country and then-President Gloria Macapagal-Arroyo declared martial law in Mindanao as the authorities attempted to track down the suspects.

The trial involved 357 witnesses and 197 suspects, 80 of them still at large.

Nicholas Bequelin, regional director at Amnesty International, said while the Ampatuans’ conviction was a “critical step” towards justice, which had stalled under three successive presidents, more needed to be done.

“The government must take steps to find and prosecute all those suspected to have taken part in the massacre,” he said. “The number of witnesses murdered during these grindingly slow judicial proceedings adds to the appalling culture of impunity.”

Emily Lopez, whose cousin, Arturo Betia, was among the media workers killed, arrived in Manila on Thursday in order to hear the verdict.

She was a mix of emotions before the decision.

“I always talk to him when I visit his grave,” she told Al Jazeera. “I tell him you’re going to get justice someday.”

With reporting by Ana Santos in Manila