Six years after gunmen flagged down a convoy of cars in the southern Philippine province and massacred all 58 occupants, relatives of the victims said Monday they are losing hope of seeing justice, especially after one of the accused was released on bail.

The Philippines' worst massacre was believed to have been political motivated, and the principal suspects are members of the Ampatuan clan, who ruled Maguindanao province for decades. The convoy carried family members of a political rival and 32 media workers, making the killings also the world's largest single attack on journalists.

The Ampatuans have denied the charges against them.

Ramonita Salaysay, widow of a slain journalist, said the release last March of suspect Sajid Ampatuan after posting 11.6 million peso ($247,561) bail for 58 murder cases was too painful and shows the unfairness of the justice system.

He is the youngest son of clan patriarch Andal Ampatuan Sr., a former Maguindanao governor, who died of a heart attack in July during his trial. The younger Ampatuan has registered his candidacy for a mayoral race in next year's election.

Late Monday, Salaysay and other relatives of victims marked the anniversary of the massacre by saying prayers and lighting candles in front of portraits of the dead at a historic bridge near the presidential palace in Manila. In southern General Santos city, relatives of other victims heard Mass at a cemetery where 12 of the slain journalists are buried.

Journalist groups also held marches to commemorate the killings and demand justice for the victims.

"My question is, is there really justice?" said Salaysay, her voice distraught. "With so many killed, Sajid paid 11.6 million pesos and immediately he was released while the conviction we are waiting for cannot be given."

She said her blood pressure rose when she heard he was freed on bail, when all along the victims expected that because the crime was heinous, bail would not be allowed.

"We felt tramped upon, it added to our pain that's why I could not move on," she said, adding that their case shows "the justice system in the Philippines is really unfair."

April Dalmacio, the eldest of three daughters left behind by journalist Leah Dalmacio, also despaired that the trial is progressing so slowly and attention on the case has waned.

She expressed fears others of the accused may find a way to be released.

Officials have said the case has been slow because of its sheer size and complexity, with nearly 200 people charged for the killings.

Presidential spokesman Edwin Lacierda said of the 197 accused, 111 have been arrested and arraigned, a total of 178 witnesses have been heard and the prosecution has already rested its case. He said the executive branch also wants to see the case resolved but can only wait for the judicial branch.

Amnesty International Philippines expressed concern that no one has been held accountable for the killing of at least eight witnesses since 2009. It added that delays and setbacks to court proceedings due to bail hearings should not be an excuse.

"Denial of justice to the victims is an affront to human rights and a mockery of justice in the country," the human rights watchdog said in a statement.