Led by Andal Ampatuan Sr., the governor of Maguindanao, the Ampatuans have controlled the province as their fief since early this decade. Because several provinces in Mindanao constitute a semiautonomous Muslim region, a provincial governor has the authority to carve up a province into smaller fiefs for his sons. New towns, along with new administrative offices and housing, can be seen along the main road cutting through Maguindanao.

But with elections scheduled for May, the Ampatuans faced a challenge for governor by Esmael Mangudadatu, the vice mayor of Buluan, a small town in this province. Significantly, Mr. Mangudadatu’s clan holds the top political positions in the province just south of here, Sultan Kudarat.

Saying that he had received death threats and that the police had denied his request for an armed escort, Mr. Mangudadatu told the Philippine news media that he had sent his wife and female relatives to file his candidacy papers before the deadline at the end of the month. He said he believed that, following traditional custom, the militias would not harm the women.

Mr. Mangudadatu also invited journalists to accompany the women on the way to Shariff Aguak, the capital of Maguindanao Province, reasoning that “maybe they will not harm us if journalists are watching them,” said Aquiles Zonio, a reporter for The Philippine Daily Inquirer who accompanied the entourage part of the way.

Felicisimo Khu, the police superintendent who oversaw the search for bodies on Wednesday, said gunmen stopped the entourage along the highway near here and drove the victims toward the hilltop along a dirt road. Another police official told national television on Monday that the force’s members were under the control of Andal Ampatuan Jr., who is the mayor of the town of Datu Unsay.

Mr. Mangudadatu said he received a phone call from his wife, Genalyn, just before she and the rest of the entourage were killed. She told him they had been taken hostage by about 100 men, he told the Philippine news media.

Image Friends, relatives and students of the victims, as well as sympathizers, lighted candles on Wednesday in Koronadal, in the southern Philippines. Credit... Jeoffrey Maitem/Getty Images

Mr. Khu said the victims were separated, men from women; vehicles were buried on one side of the hill and the victims on the other. The gunmen seemed to have stayed a long time on the hilltop, as suggested by cooking pots found at the scene.