Police have arrested three of the four suspects in the killing of American marine biologist Dr. Kent Carpenter with the authorities ruling out any link to his scientific work, including his contribution to the Philippines’ landmark 2016 South China Sea arbitral victory.

Philippine National Police spokesperson Col. Allen Rae Co announced Thursday the suspects were in custody, identifying them only by their initials: M.O., the alleged gunman; J.F., who allegedly sexually assaulted Carpenter’s partner; and C.D., who allegedly served as the lookout.

The fourth suspect, known only as “Eden,” remains at large. Police said the suspect allegedly fled with the stolen valuables, prompting authorities to pursue charges of robbery with homicide.

Carpenter, 73, was shot dead late Sunday after armed men forced their way into his home in Barangay Ajong, Sibulan, Negros Oriental. Investigators said he was watching television when he was shot in the head.

PNP chief Gen. Jose Melencio Nartatez Jr. commended investigators from the Police Regional Office–Negros Island Region, the Negros Oriental Police Provincial Office, and the Criminal Investigation and Detection Group for the swift arrests but ordered intensified operations to capture the remaining suspect.

“The swift arrest of the three suspects reflects the dedication and professionalism of our investigators, but our work is far from over,” Nartatez said.

Inside job?

Based on the investigation, police believe the crime was a robbery that turned deadly. One of the suspects had reportedly worked at Carpenter’s residence and was familiar with the property.

Authorities are also checking whether the suspects were involved in previous robberies in the area.

Carpenter’s female partner was initially tagged as a “person of interest” after a test to determine whether she had been raped yielded a negative result.

Valuable contributions

The Department of Environment and Natural Resources paid tribute to Carpenter, describing his death as a profound loss to the scientific community.

Environment Secretary Juan Miguel Cuna said Carpenter devoted decades to advancing marine biodiversity research in the Philippines, working closely with Filipino scientists, including National Scientist Angel Alcala.

Among his major contributions were pioneering studies on the Tubbataha Reefs and the Verde Island Passage, whose extraordinary biodiversity earned global recognition. His research also helped strengthen marine protected area management and fisheries conservation in the country.

Carpenter also served as an expert witness in the South China Sea arbitration, documenting the environmental damage caused by dredging and coral reef destruction in the West Philippine Sea.