An American marine biologist whose landmark research identified the Verde Island Passage as the world's "Center of Marine Shore Fish Biodiversity" was shot dead inside his home in Sibulan, Negros Oriental, on Sunday night, the Philippine National Police (PNP) said Tuesday.

The victim was identified as Dr. Kent Carpenter, 73, an adjunct professor and associate researcher at Silliman University.

Police said Carpenter was watching television with his 34-year-old Filipina companion at around 11:30 p.m. on 12 Julywhen three unidentified men wearing bonnets forced their way into the house in Barangay Ajong.

Capt. Mary Jean Gutierrez, chief of the Sibulan Police Station, said Carpenter was shot in the head and died at the scene. His companion was unharmed.

Authorities have launched a manhunt for the suspects and are investigating the motive behind the killing.