Manila, Philippines (CNN) -- Filipinos on Tuesday marked the first anniversary of what are considered the worst politically motivated killings in recent Philippine history.
President Benigno Aquino declared November 23 a national day of remembrance for the dozens of victims. He wore a black commemorative armband on Tuesday.
A march was planned to retrace the path of the victims' doomed convoy, which was ambushed on November 23, 2009.
Tuesday's march is part of what Filipino journalists and their supporters also have declared Media Freedom Day.
The wife and sister of a political candidate and 30 journalists were among the dozens of victims who were shot and buried in a mass grave. At least 57 people died in the ambush. A search has not yielded the body of another presumed victim.
A powerful political family has been implicated in the massacre in Maguindanao province, in the southern Philippines.
Andal Ampatuan Jr. -- former mayor of Maguindanao and the son of a former provincial governor -- is now on trial, accused as the ringleader of the massacre. The key targets were allegedly the wife and sister of a political rival of Ampatuan's.
Ampatuan and his family have denied wrongdoing.
On Tuesday, soldiers quietly stood guard during prayers in honor of the dead.
In Manila, a sea of black filled the streets as thousands of media workers wearing black shirts paraded around the city chanting, "justice for the Ampatuan massacre victims" and "justice for journalists."
There are 196 accused, about 500 witnesses and more than 11,000 murder charges involved in the massacre case, which is expected to take years.
As part of Tuesday's march, what was called a Caravan for Justice was to leave from four points in the Philippines -- Davao City, Kidapawan City, General Santos City and Marbel, South Cotabato, according to CNN television affiliate ABS-CBN.
Philippine Justice Secretary Leila De Lima was expected to take part in the day's commemorative events, which were to include forums on problems affecting media.
"We need to redeem the day by launching the freedom day," said lawyer Carlos Zarate, of the Alliance Against Impunity in Mindanao.
He also urged the public to be vigilant about the slow progress of the massacre case.
"We should learn lessons from it, so those victims will not have died in vain," Zarate told ABS-CBN. "We should not leave it to court alone and not be complacent."
The massacre shocked people even in a country that is familiar with election violence.
The trial of Ampatuan and his alleged accomplices has been delayed repeatedly. The postponements have prompted outcries against the political influence of the Ampatuan family. They have ruled Maguindanao for two decades.
Maguindanao is part of an autonomous region in predominantly Muslim Mindanao, which was set up in the 1990s to quell armed uprisings by people seeking an independent Muslim homeland in the predominantly Christian Asian nation.
Journalist Winona Cueva contributed to this report.