American biologist shot dead in his home in the Philippines

73-year-old American biologist Kent Carpenter was shot and killed at his home in the Philippines on Sunday in what authorities are calling a murder.

Carpenter, an adjunct professor at Silliman University's Institute of Environmental and Marine Sciences in Dumaguete City, was in his home with a 34-year-old girlfriend when authorities say three men broke in at 11:30 p.m.

One of the men allegedly shot Carpenter in the head during what police believe was a robbery. The men also allegedly tied up Carpenter's girlfriend and sexually assaulted her, the government-affiliated Philippine News Agency (PNA) reported.

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The men took a laptop, cash and a backpack before fleeing, police spokesperson Col. Allen Rae Co told reporters.

All three of the suspects are still at large, though local police have initiated a special investigation to find the culprits, PNA reported.

Local investigators began "conducting backtracking and forward tracking operations, including the review of possible CCTV footage, witness interviews, intelligence validation, and reconstruction of the suspects’ movements before and after the incident," police wrote in a statement.

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"We strongly condemn this senseless act of violence. I have directed our investigators to exhaust all legal means to identify and apprehend those responsible at the soonest possible time," Regional Director Police Brigadier Gen. Romano Cardiño said in the statement.

"We assure the victim’s family, the community, and our foreign visitors that this case is being treated with utmost urgency, and no effort will be spared until justice is served," he also said.

Carpenter was a highly renowned scientist who studied fish, co-authoring a 2005 study that crowned the Philippines' Verde Island Passage as "the center of marine shore fish biodiversity."

He spent decades working as an ichthyologist, collaborating with Silliman University in some capacity since 1976.

"Dr. Carpenter made groundbreaking contributions that transformed global understanding of Philippine marine biodiversity," Silliman University said in a statement.

"Dr. Carpenter's contributions to Philippine marine science were profound and enduring," a statement the Philippine Association of Marine Science posted Tuesday read.

"As a U.S. Peace Corps volunteer in the 1970s, he worked with the Bureau of Fisheries and Aquatic Resources and helped train the country's first coral reef science team. His early papers on Philippine coral reef fisheries resources, including his work with National Scientist Angel C. Alcala on muro-ami and kayakas reef fisheries, were landmark contributions that shaped the country's understanding of reef fisheries and the urgent need for science-based management," the statement continued.

"In the wake of this devastating loss, PAMS strongly condemns this act of violence. We call upon the Philippine National Police, the local authorities in Negros Oriental, and appropriate national investigative agencies to conduct a swift, thorough, and transparent investigation. Those responsible for this heinous crime must be held fully accountable under the law," the statement added.

"Dr. Carpenter devoted his life to protecting the Philippines' marine heritage. We owe it to him to honor that legacy by continuing his work and demanding justice for his tragic and untimely death," the statement concluded.

Fox News Digital contacted the U.S. Embassy in Manila for further comment.

The Associated Press contributed to this report.