Government prosecutors filed 16 more murder charges Monday against the member of a powerful clan who allegedly led last month's massacre of political rivals and journalists in the southern Philippines. At least 57 people were brutally killed with guns and machetes, many of their bodies buried by backhoe, on Nov. 23 in southern Maguidanao province. One body remains unidentified, preventing an indictment, but Andal Ampatuan Jr., a town mayor, has now been charged with the other 56, senior state prosecutor Leo Decera III said. Among those killed were 30 journalists and their staff in what is considered the deadliest single attack ever on media workers. The carnage has sparked international outrage, prompting President Gloria Macapagal Arroyo to briefly impose martial law in Maguindanao that she said was needed to crack down on the powerful Ampatuan clan, a key political ally. Ampatuan's father, who heads the clan, and several other close relatives have also been accused of involvement in the killings but have yet to be indicted. The clan have denied any role in the massacre. The International Crisis Group, a prominent Brussels-based think tank, said Monday that Arroyo's political backing of the Ampatuans, who helped her win crucial Maguindanao votes during the 2004 elections, has allowed the warlord clan to flourish dangerously for years in Maguindanao, a predominantly Muslim province about 560 miles (900 kilometers) south of Manila. Arroyo's administration allowed “a local despot” to “amass great wealth and unchecked power, including the possession of a private arsenal ... in exchange for votes at election time,” the ICG said. Arroyo's aides have acknowledged her close alliance with the Ampatuans but said that did not authorize the clan to commit any crime. The Ampatuans were expelled from Arroyo's ruling party after the killings. The victims were traveling in a convoy led by the family and supporters of the Ampatuans' election rival when they were allegedly stopped by Ampatuan Jr. and about 100 militiamen, led at gunpoint to a grassy hilltop then shot and hacked to death.Ampatuan Jr. surrendered after the killings and is detained under heavy guard in Manila.