MANILA, Philippines (CNN) -- Authorities have filed murder charges against a politician over the massacre of 57 unarmed civilians in the Philippines, state-run media reported Thursday.
Andal Ampatuan Jr, who is the mayor of the town of Datu Unsayalso and the son of a Philippines provincial governor, had voluntarily turned himself in for questioning Thursday.
It was not immediately clear how many murder charges Ampatuan would face in Monday's massacre in Maguindanao province, in the southern Philippines.
Five other people believed to be connected to the massacre were also being prosecuted, the state-run Philippines News Agency reported.
This group includes three police officers, the agency reported.
The government of President Gloria Macapagal-Arroyo was under intense pressure to find those responsible for planning and carrying out the abduction and killing of the group of journalists, lawyers and a politician's family members.
Suspicion had fallen on the Ampatuan family, key allies of the Arroyo administration in the Maguindanao region of southern Mindanao province.
The massacre is the worst politically motivated violence in recent Philippine history, the news agency said.
On Monday morning, a group of about 100 gunmen stopped a convoy carrying supporters and family members of politician Ismael "Toto" Mangudadatu, witnesses and officials say.
Mangudadatu had sent his wife and sisters to file paperwork allowing him to run for governor of Maguindanao in May after he had been threatened and told not to file the papers himself. He said the threats came from allies of Maguindanao Governor Andal Ampatuan, the father of the accused mayor.
The exact number of those kidnapped and killed was still unclear, as recovery continued at a mass grave site in Maguindanao.