Manila, Philippines (CNN) -- One hundred more suspects -- including police officers -- could face arrest over a massacre in the Philippines, a government official said Friday after authorities charged the alleged architect of the killings.
At least 57 unarmed civilians were slain Monday in Maguindanao, in the southern Philippines. Andal Ampatuan Jr. -- mayor of Datu Unsay and son of the provincial governor of Maguindanao -- faces seven counts of murder.
Justice officials said they have collected sworn statements from witnesses and expect to file more charges as the investigation unfolds.
Witnesses have implicated dozens of people in the election-related killings, said Philippine Interior Secretary Ronaldo Puno.
"There are an estimated 100 people that will be brought to account for this incident," he said. "We are in the process of preparing cases against them and ultimately filing similar charges. These people are actually members of the police in the province and civilian volunteers in the province."
Speaking to state-run television from behind bars, Ampatuan denied any involvement, CNN affiliate ABS-CBN news reported Friday.
Meanwhile, police were on alert to prevent further violence, ABS-CBN said.
Violence in the run-up to elections -- the next set for May -- is not uncommon in the Philippines. The Maguindanao massacre, however, is the worst politically motivated violence in recent Philippine history, according to state media.
Ampatuan voluntarily turned himself in for questioning Thursday, then was charged.
In the subsequent television interview, he blamed Moro Islamic Liberation Front (MILF) commander Umbra Kato as the possible architect of the massacre.
Puno on Friday rejected that allegation.
"At the moment, there is no evidence that the Moro Islamic Liberation Front had anything to do with this," he said.
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.
Negotiations between the MILF, which is one of those armed groups, and the Philippine government broke down last year after the country's Supreme Court blocked a peace deal that would have increased the size and scope of the autonomous region.
The MILF lashed out at Ampatuan over his accusation, calling it a "clear attempt to divert the issue," ABS-CBN reported.
Suspicion fell on Ampatuan after a government construction vehicle was found at the hastily dug mass grave where the massacre victims' bodies were found.
Among the victims were the wife and sister of Ismael "Toto" Mangudadatu, who had sent the women to file paperwork allowing him to run for governor of Maguindanao. He said he had received threats from allies of Gov. Andal Ampatuan, the father of the accused mayor, saying he would be kidnapped if he filed the papers himself.
Also killed were a dozen journalists who had accompanied the women.
Witnesses and local officials have blamed Ampatuan, a longtime ally of Philippines President Gloria Macapagal-Arroyo and a known warlord.
They said the killings were an attempt to block Mangudadatu from challenging him in the gubernatorial election.
The exact number of those kidnapped and killed was still unclear, as recovery continued at the mass grave site.
Journalist Steve Lunt in Manila contributed to this report.