An American environmentalist who dedicated his life to marine conservation in Japan has died in a suspected suicide, police said Sunday.

Jack Thomson Moyer, 74, was found dead Saturday at his home in Tokyo by a friend, a Tokyo Metropolitan police spokesman said on condition of anonymity.

Two letters, one addressed to his wife in the Philippines and another addressed to a friend with whom he had worked closely, were found along with some 400 pills, according to local media reports.

No further details were available.

Moyer, originally from Kansas, spent more than 50 years studying the dolphin populations and coral reefs near Miyake Island, 190 km south of Tokyo.

He was temporarily forced to flee the island, along with about 4,000 other residents, in September 2000 when a volcano there erupted several times.

After arriving in Japan in 1951 with the U.S. military, he worked to protect the country's natural coastline and reefs, taught science at a foreign school in Tokyo and ran a series of educational workshops attended by students from across the nation.