Tokyo ? Japanese police were investigating possible negligence by tour organizers after 10 senior citizen climbers were found dead Friday in Japan’s northern mountains, apparently from hypothermia.

Nine seniors died while climbing Mount Tomuraushi on Hokkaido, Japan’s main northern island, said police spokesman Masafumi Yamasaki. Eight were part of an 18-member group tour organized by Amuse-Travel Co. Ltd., while the other was climbing alone.

A 10th elderly person died on another mountain on Hokkaido, he said.

Another police official, Tsuyoshi Matsuya, said investigators believe almost all the victims died of hypothermia.

“We are looking into a possibility of professional negligence on the part of organizers,” Matsuya said.

Investigators believe the elderly climbers, caught in strong winds and worn out, quickly deteriorated as chilly mountain air and rain sent their body temperatures dangerously low.