The three arrived in Sulu on a ferry from Zamboanga City on Sunday but were immediately seized by armed men on motorcycles, local Army chief Col. Alexander Yapching said.
The gunmen took the three to the town of Patikul, a known base of the Abu Sayyaf, a band of Muslim extremists engaged in kidnapping foreigners and Christians and other acts of banditry for over a decade.
The decomposing bodies of the three, bearing gunshot wounds, were reported found on Thursday.
Yapching would not discuss any motive for the killings or say if they were believed to be the work of the Abu Sayyaf, which has been linked by both Washington and Manila to the al-Qaeda network of terror mastermind Osama bin Laden. — AFP, Roel Pareño