Iraqi police on Saturday found eight severed heads north of Baghdad with a note indicating at least one of the men were killed in retaliation for the slaying of four Shiite doctors, authorities said. Five of the slain men were security guards at a hospital complex in the capital who had been arrested by Iraqi police on Thursday, Lt. Col. Adil Al-Zihari of the Diyala police said.Notes found with the heads near a highway in the Hadid village near the volatile city of Baqouba, 60 kilometres northeast of Baghdad, said one of those killed was Abdul Aziz al-Sheik Hamad and accused him of killing four Shiite doctors and a former governor during the administrator of former Prime Minister Ayad Allawi. The heads were transferred in fruit boxes to the morgue in Baqouba, a mixed Sunni Arab-Shiite town that has recently seen an increase in sectarian violence.