Choi Inn-so, 52, died in a hospital in southern Cagayan de Oro city last week after undergoing surgery. He was abandoned by his kidnappers Nov. 24 in Lanao del Sur province, said Cagayan de Oro police chief Gerardo Rosales.

Quoting Choi’s doctor, Rosales said the businessman developed an infection in his lungs, kidneys and heart. It was possible he got sick while in captivity, he said.

Choi’s body will be autopsied and police were coordinating with the South Korean Embassy, Rosales said.

Ransom kidnappings have long been a problem in the southern Philippines. Separatist rebels, terrorist groups and criminals operate in many parts of the Mindanao region, but it was not clear what group was responsible for the latest abductions.

The three Koreans and their Filipino guide were kidnapped Oct. 21.

The military has said Choi was apparently released because he was ill and slowing down the group. The two other South Koreans were released two days later, after troops closed in and the gunmen panicked.

Rosales said the body of the Filipino guide was recovered late last month and the kidnappers remain at large.

Army Col. Daniel Lucero has said the kidnappers demanded up to 50 million pesos ($1.2 million) in ransom but received nothing.

Another military official, Maj. Gen. Noel Coballes, said that the kidnappers apparently lured the South Koreans with a nonexistent mining investment project.