Philippine police are investigating the murder of a 54-year-old Japanese man whose body was found buried in a shallow grave Saturday in one of the islands off Alaminos City north of Manila, police said Sunday.

Police officer Amandao Muena identified the victim as Tsutomu Hiraga of Saitama Prefecture. He said another Japanese man, Mitsuaki Sato, 59, also from Saitama, and local tourist guide Dennis Dumangcang, 35, have been taken into custody in connection with Hiraga's death.

"We suspect that Hiraga was poisoned," Muena said, adding the motive for the killing hasn't been determined.

The police said Sato arrived in Manila on Tuesday, and on Friday he and Dumangcang hired a car that took them to Alaminos, where they checked into a hotel.

Hiraga then headed directly to Sato's hotel room, where they had a meeting. The police said Hiraga, Sato and Dumangcang then hired a motorboat and headed to Camantiles Island, where Hiraga's body was found buried in a 30-cm-deep grave at around 1:30 p.m. Saturday.

The police said Sato initially told officers that Hiraga felt dizzy on the boat and subsequently died upon arrival at the island. Sato told the police that he was scared and decided to just bury Hiraga there.

"We don't believe his (Sato's) statement because Hiraga's hands were bound by a rope," police officer Muena said.