Police are looking for a man who may have been involved in the death of a U.S. Peace Corps volunteer in a mountainous tourist area in the northern Philippines, officials said Thursday.

Regional police chief Raul Gonzales said that a witness claimed he saw a man in the area of the shallow grave in Banaue township where Julia Campbell's body was found on Wednesday, 10 days after she went missing. Police suspect foul play.

Senior Superintendent Pedro Ganir, police chief of Ifugao province, which includes Banaue, said the man was the husband of a woman who sold a Coca-Cola to Campbell before she headed off on a hike in the area's famed mountainside rice terraces, a World Heritage site.

Ganir said investigators were looking into "robbery with homicide or rape with homicide," although an autopsy on Campbell's body has not yet been carried out.

He said officers also recovered her other belongings scattered near the body, including coins and clothes.

Jun Addug, a Banaue councilor, said the witness was a 13-year-old boy.

The man police are trying to find allegedly rushed down to a dry creek when he realized the boy had spotted him, municipal council member Jun Addug said after speaking with the teenager.

The boy, who did not see Campbell, later saw the same man going back up to the trail from the creek, Addug told The Associated Press by telephone from Banaue.

The man has been missing since, Addug said.

President Gloria Magapagal Arroyo's spokesman, Ignacio Bunye, said the government was cooperating with U.S. officials in the investigation.

"It is unfortunate that a committed and selfless person who has ... obviously grown to love our country met a tragic end here," Bunye said in a statement.

Soldiers searching for Campbell — a freelance journalist who had reported for The New York Times and other media organizations — found one of her feet sticking out from the shallow grave in the dry mountain creek in Banaue.

Army Maj. Gen. Rodrigo Maclang said soldiers reported the body was covered with soil, gravel and grass.

Campbell's body was flown to Manila for an autopsy. The U.S. Embassy said the Philippine government will disclose the cause of death.

A team of U.S. forensic pathologists based in Japan will arrive Saturday to observe the autopsy, said Geary Barias, chief of the police Directorate for Investigation and Detective Management.

Peace Corps Director Ron Tschetter said Campbell, who was among 137 volunteers currently in the Philippines, "contributed greatly to the lives of Filipino citizens."

"Julia was a proud member of the Peace Corps family, and she contributed greatly to the lives of Filipino citizens," Tschetter said in a statement. He described her as "a dedicated and vibrant volunteer, who so loved this country."

He had traveled to the Philippines to join the search for Campbell, and he praised the local police effort to find her as "incredible."

In a statement, Campbell's family in Fairfax, Va., said she "lived a very full life."

"She loved her family and friends and is much loved. She was passionate in her journalism reporting especially the stories involving people who were able to stand and address adversity or adverse situations," the statement said.

"We have every confidence that the U.S. and Philippine authorities are conducting a thorough investigation into Julia's untimely death."

Campbell had been teaching English at the Divine Word College in Albay province's Legazpi city, southeast of Manila, since October 2006.