Manila, Philippines (CNN) The men who planned a massacre which rocked the Philippines' political establishment more than a decade ago have been found guilty of murder.

On November 23, 2009, 58 people were killed in the town of Ampatuan, in the southern province of Maguindanao. Their bodies were buried in three shallow graves on a hilltop.

The wife and sister of political candidate Ismael "Toto" Mangudadatu and 30 journalists were among the victims.

Mangudadatu had sent his family members to file paperwork allowing him to run for governor of Maguindanao.

Their convoy was ambushed, sprayed with bullets -- after which the survivors were ruthlessly hunted down and executed.

Mangudadatu was running to end the 20-year rule of the Ampatuan family. His rival in the election was Datu Andal Ampatuan, Jr., also known as Unsay, mayor of Datu Unsay town, and son of the incumbent governor, Andal Ampatuan, Sr.

On Thursday, a judge in Manila found Ampatuan Jr. -- along with several other relatives and primary suspects -- guilty on multiple accounts of murder. They were sentenced to life in prison.

"This is momentous verdict should help provide justice to the families of the victims, and build towards greater accountability for rights abuses in the country," said Phil Robertson, Deputy Asia Director, Human Rights Watch."

"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. More broadly, 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."

Members of the police special action force stand guard at a gate of the capital command headquarters in Manila on December 19, 2019.

The scandal resulted in an end to the Ampatuans grip on politics in Maguindanao.

Toto Mangudadatu became governor in May 2010, according to CNN Philippines , six months after the massacre. He served three terms before running successfully for Congress this year.

Speaking to CNN Philippines, Mangudadatu said he could "forgive" those responsible, "but still, we will look for justice. We can let it go, but we need justice."

Supporters and journalists hold a rally in front of the gate of the capital command headquarters in Manila on December 19, 2019.

It had been dubbed by many in the Philippines media as the "trial of the decade." Of the 197 people eventually charged with murder, eight have died during the long procedures, including Andal Ampatuan Sr. Some 80 suspects still remain at large. Thursday's trial involved 101 suspects, including those who planned the massacre.

"We know who we have a strong case against," Nena Santos, lawyer for the families of 38 victims, told CNN Philippines ahead of the verdict. "There are some whose involvement in the conspiracy was not established so I think they will be freed like some of the policemen who were just assigned there and knew nothing but were included in the charges."

The failure to bring all suspects to trial, including several dozen police officers and soldiers, could yet put the family members of victims and witnesses at risk, Human Rights Watch has warned

"The families of Maguindanao victims and witnesses will be at risk so long as suspects remain free," said Robertson. "Regardless of the verdicts in the case, Philippine authorities need to apprehend the several dozen suspects still at large."

HRW said some suspects at large had sought sanctuary with rebel groups operating in the area. Maguindanao is located on the southern island of Mindanao, which has long been a hotbed of insurgency against the Manila government.

Mindanao sits at the borders of Malaysia and Indonesia, and has been plagued by terrorism and unrest. It is home to several Islamist insurgent groups, including Abu Sayyaf, which has been blamed for a number of attacks on civilians and Philippine government troops, as well as the kidnapping of several foreign nationals.