In this Feb. 27, 2016, photo provided by the Philippine National Police Barobo Station, a man's remains is seen on a yacht near the shore off Barobo township, Surigao Del Sur province in southeastern Philippines. Philippine police say they're trying to determine the identity and cause of death of a sailor who was found dead while sitting slumped on a table by the radio of a wayward yacht found adrift in the Pacific Ocean. (Christopher Templanza/PNP Barobo Station via AP) MANDATORY CREDITThe unusual death of a presumed German adventurer, found mummified-looking in a damaged yacht drifting in the Pacific Ocean, has authorities struggling to uncover the man’s last known whereabouts.

The gray decomposing remains were found in a seated position, slumped over a desk next to the boat’s radio, quickly succumbing to the intense heat and dry ocean air last week. The cause of death remains unknown.

Authorities have not yet determined the post-mortem interval, but Philippine authorities have said the man was dead for at least “several days,” and are awaiting an autopsy report expected later this week.

Documents aboard the boat identified the owner of the boat as a missing 59-year-old German adventurer, Manfred Fritz Bajorat—likely the identity of the decedent, according to local police.

Chief Inspector Dominador Plaza told the Associated Press the man appeared to die quickly, and there were no apparent signs of foul play.

“Initially, it looks to us that he died of natural causes, maybe a heart attack,” he said. “And death appears to have come suddenly because he was still sitting by the table when he passed away.”

Investigators are trying to track down the missing man’s last known whereabouts, although reports said he has not been seen since 2009—a year after he split with his wife, and travelling companion, who later died of cancer.

Media outlets also reported about a “thirty-two word memorium” to his wife found near the remains, although those claims could not be independently verified.

According to the Barobo Police Station, the yacht was discovered by a 23-year-old fisherman on his way home, last Friday afternoon. The man boarded the ship, and noticed the mummified body, where he called his companions to help him tow the ship to the police.

A local mayor said a daughter of Bajorat called to inform authorities that the family was planning to travel to the Phillipines to help identify the body, and that they planned to have the body cremated before bringing the remains back home, according to the report.

The Associated Press contributed to this reporting.