Major Randolph Cabangbang, spokesperson of the military's Eastern Mindanao Command said Alston is investigating the spate of killings of members of militant and party list organizations and journalists.
Kelly Delgado, Karapatan Southern Mindanao secretary general, said Alston will meet with their members from around Mindanao together with witnesses, survivors, and relatives of victims.
He said he Alston will meet them for at least five hours in an undisclosed venue. He said the witnesses and relatives of victims agreed to surface on condition they will not face the media.
Alston is in the country on a 10-day official visit a year after leaders of human rights groups went to the United Nations to lobby for an investigation, Delgado told MindaNews.
The military's Civil Relations Service warned Alston's visit would be met by mass actions by groups they labeled as "CPP/NPA front organizations" .
Cabangbang said the groups will launch mass demonstrations in time for the visit. Delgado said the alleged mass action may have been a spin by the military so they can justify the deployment of forces and harass the witnesses and victims to dissuade them from testifying to Alston.
He said presentation of evidence is an even bigger blow to the government than a mass demonstration.
Cabangbang said the military welcomed Alston's visit. The Eastern Mindanao Command, tasked to stop communist insurgents this part of Mindanao, has welcomed the visit with a pledge that military commanders will extend assistance for the visitor "to see the real situation in Mindanao".
Major Medel Aguilar, CRS group commander, told MindaNews Alston is scheduled to meet with officials from the Philippine National Police and the Armed Forces of the Philippines, and leaders of other government offices.
Another source, who asked not to be quoted, said the UN official will have met with officials from the National Bureau of Investigation, the Commission on Human Rights, and the Department of Justice.
He said the Department of National Defense is coordinating with Alston, Karapatan said Alston is also due to include in his probe summary killings in Davao City including cases involving children and drug related incidents.