The Philippine government must urgently ensure that witnesses are protected following the massacre of at least 57 people in Maguindanao province and safeguard vital forensic evidence to ensure those responsible are brought to justice, said Amnesty International.
Datu Unsay Mayor Andal Ampatuan Jr, a member of the powerful Ampatuan family that has dominated local politics in Maguindanao province in the country's restive Mindanao region, is now under arrest and could face multiple murder charges. He has denied involvement.
"One of the major stumbling blocks to justice for human rights violations in the Philippines has been the intimidation of witnesses, at times accompanied by bribes or other inducements," said Donna Guest, deputy director of Amnesty International's Asia-Pacific programme.
"Given the Ampatuan family's history of using private militias to maintain their dominance in Maguindanao, there is every reason to fear for the safety of witnesses and the protection of evidence."
Amnesty International pointed out that the inability of Philippines investigators to gather and process forensic and circumstantial evidence in prosecutions has led to an overreliance on eyewitness testimony.
Media footage from the scene of the massacre shows little evidence of proper collection of forensic evidence.
"The Philippine government has responded with encouraging speed and seriousness to this incident so far but they must demonstrate that they will put in place proper mechanisms to ensure there is transparent, credible accountability," Guest said.
"This case, which has shocked the country and the world, cannot end in impunity as the vast majority of cases of political killings have in the past."
Amnesty International called on the government of the Philippines to invite assistance from the international community in conducting the technical aspects of this investigation.
The European Union and the Philippine government have recently signed an agreement to improve the quality of investigations and prosecutions of extrajudicial executions in the Philippines.
Most witnesses are reported to lack confidence in the current witness protection program, and fear that, given prolonged delays in criminal proceedings, it will not be able to offer protection to them or their families which may be needed to extend over a number of years.
In conjunction with lack of confidence in the impartiality of the police, fear of reprisals and a lack of an effective witness protection program, most investigations remain ineffective and fail to lead to the identification, arrest, trial and conviction of the perpetrators.