The Philippines is marking the fifth anniversary of the country's worst political massacre, which left 58 people dead.
The victims, including reporters, were killed after their convoy was attacked in southern Maguindanao province.
More than 100 suspects are standing trial for murder, some of them members of the powerful local Ampatuan clan. They deny the charges.
Amnesty International says the trials risk becoming "a mockery of justice".
"Justice delayed is justice denied," said Hazel Galang-Folli, Amnesty's Philippines researcher.
"Five years after the Maguindanao massacre, the cases are still inching through the Philippine court system and not a single person has been held to account."
The 23 November 2009 massacre is alleged to have been carried out by the Ampatuan clan to stop a political rival from running for the post of governor.
The clan's candidate, Andal Ampatuan Jnr, allegedly led his family's private army in stopping a convoy carrying his foe's wife, relatives, lawyers and a group of more than 30 journalists, and then gunning them down.
The victims' bodies were later found in a mass grave in a secluded mountainous area of the province.
Andal Ampatuan Jnr, his brother and their father are among 111 suspects on trial.
However, court officials say many suspects are still at large, and prosecutors do not expect the court to hand down verdicts until next year at the earliest.
Since the beginning of the trial in 2010, four witnesses have been killed.