(CNN) -- An alleged ringleader in what is considered the worst politically motivated killings in recent Philippine history is expected to go on trial in Manila on Wednesday.
The mayor of Maguindanao province, Andal Ampatuan Jr., and his alleged accomplices are to stand trial in the November 2009 massacre in Maguindanao. Andal Ampatuan Sr. -- the former provincial governor and the father of Ampatuan Jr. -- also has been charged in the killings. In all, about 200 suspects have been arrested in the attack.
An investigation has revealed a well-planned conspiracy, in which members of the Philippine police and army also were involved, said an eight-member commission of the justice department.
"The confluence of events before and immediately after the massacre took place led us to conclude that (the governor, his son and others) connived with the actual perpetrators," the commission said earlier this year, according to the state-run Philippines News Agency.
The wife and sister of political candidate Ismael "Toto" Mangudadatu and 30 journalists were among the 57 victims. Mangudadatu had sent his family members to file paperwork allowing him to run for governor of Maguindanao. Their convoy was ambushed, allegedly by the Ampatuans and their associates. The 57 bodies were recovered -- some had been shot assassination-style, others died when their vehicles were sprayed with bullets.
The massacre shocked people even in a country that is familiar with election violence.
The trial of Ampatuan Jr. and his alleged accomplices has been delayed repeatedly, most recently because of a defense request for more preparation time. The delays have prompted outcries against the political influence of the Ampatuan family. They have ruled Maguindanao for 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.