By Vaudine England
President Arroyo has promised justice for the massacre victims
When news of the killings first trickled in, Philippine President Gloria Arroyo was just six months away from relinquishing office after nine years in power.
Many had thought her primary concern was to secure a succession that would keep her safe from possible litigation over several corruption allegations.
But then a member of one her closest allies in the south - the Ampatuan family - was linked to the shocking murders of 57 people in Maguindanao, a province on the large island of Mindanao.
The victims were mainly women and journalists, in what appears to be election-linked clan violence.
Mrs Arroyo has vowed to bring the killers to justice. Black ribbons are tied to the gates of her official residence in Manila, Malacanang Palace.
The prime suspect, Andal Ampatuan Junior, is in detention in Manila.
Scores of gunmen and even some senior policemen have been detained in Maguindanao, which the Ampatuan family has long controlled.
"The judicial process will progress very quickly in this case," believes Alex Magno, professor of political science at the University of the Philippines.
"The private army has been disbanded, the military has taken over the provincial government, the Ampatuan family is now off the political map and can't even file their candidacies" for the 2010 elections, said Mr Magno.
"Justice will come as a matter of political expediency," he said.
But there will be a strategic price to be paid by future governments, he believes.
The military has moved soldiers into Maguindanao from nearby provinces, leaving them open to one of the Islamist separatist groups, the Moro Islamic Liberation Front.
Mindanao has long been home to several overlapping Muslim and communist insurgencies which, though not involved in the latest massacre, have influenced the political makeup of the area.
Chief suspect Andal Ampatuan Jr - behind bars in Manila
Their presence has stretched the military, leading to the creation of civilian volunteer groups which have then been armed and often paid by powerful families to act as their own private armies.
It is these paramilitaries who are suspected of carrying out the killings, on orders from clan leaders.
"Maguindanao is a particularly toxic mix," said Sheila Coronel, founder of the Philippine Centre for Investigative Journalism and a professor of journalism at New York's Columbia University.
But the pattern of a weak central government and the failure of the courts, army and police to stand up to provincial powers is seen across the country.
The problem has worsened under Mrs Arroyo's presidency, said Ms Coronel.
"Her government has a track record for cultivating impunity - there have been more political killings during her term than in the last 20 years," she said.
This feeds a widespread scepticism that justice will be done. Many Filipinos appear convinced the killers will get off with short times behind bars or negotiated settlements.
Amina Rasul, director of the Philippine Centre for Islam and Democracy, noted that when Andal Ampatuan Jr was brought to Manila he was not handcuffed.
"People see this and it compounds their belief that nothing will happen," Ms Rasul said.
"When your credibility is at stake, the least she should do is go by the letter of the law," she said of President Arroyo.
Face saving for the powerful families is just one aspect of the broader negotiations required if Mrs Arroyo wants to serve out her term, believes Ms Coronel.
"She needs military support to continue in office and there have been some very frustrated military factions trying to unseat her, so she has won the support of the top brass by allowing unorthodox methods, particularly against communist insurgents," said Ms Coronel, referring to alleged extra-judicial killings and abductions in recent years.
This is because Mrs Arroyo first came to power through a so-called "People Power" movement which required military support to succeed.
Many of the victims were buried in hastily-dug mass graves
"It's an indication of the compromises and alliances she has had to make to stay in power. She is reaping the whirlwind," said Ms Coronel.
The justice department could not be reached for comment, but an under-secretary for justice, Ricardo Blancaflor, has previously told the BBC that allegations of extra judicial killings and impunity under the Arroyo government are "not true, not true at all".
Mr Blancaflor oversees a task force dedicated to solving at least 40 cases of journalists being killed in the Philippines. He said all cases were proceeding against identified killers and would be pursued with the full vigour of the law.
The question now is: will the scale of this mass murder be enough to jolt the political class into a new vigilance against murder and corruption on the campaign trail?
Or will the run-up to the national and local elections in May 2010 offer a spiral of violence and revenge killings?
"I would like to imagine that at least a few senior politicians woke up this week to seriously wonder what kind of monsters they and their system have created over the years," said Alan Davis, Asia director for the Institute of War and Peace Reporting and Director of the Philippine Human Rights Reporting Project.
"President Arroyo has reportedly been looking around for her legacy and the best mark of her nine years in power. The Maguindanao massacre is most surely it," Mr Davis said.
"For once the authorities acted. But then given the scale, this time they couldn't afford not to."