Four teens were arrested Friday on suspicion of vandalism at a cave in Okinawa Prefecture where civilians were forced to commit mass suicide in the closing days of World War II, police said.

The boys aged 16 to 19 have admitted to destroying with sticks two signboards and origami paper cranes left by visitors to the Chibichirigama cave in the village of Yomitan last Sunday, saying they went to "a haunted spot" on a motorbike to "test their courage," according to investigators.

During the Battle of Okinawa, which started on April 1, 1945 with the landing of U.S. forces on the southern Japanese island, more than 80 Okinawa residents were believed to have committed suicide in the cave after taking refuge there. Similar cases of mass suicide of civilians occurred at other locations during the battle, although exact data is unavailable.

Family members of those who killed themselves during the war at the site discovered the damage last Tuesday at the cave, a local cultural property, and reported it to the police.

The four emerged as suspects after investigators checked security camera footage and interviewed neighbors, according to the police.

Norio Yonaha, 63, who lost five members of his family in the mass suicides and heads the group of bereaved families, has told reporters the vandalism was "an insult to the people who died" at the site.

Bottles and vases left by the wartime civilian victims at the cave were also found to have been damaged.

Some 94,000 civilians, or about a quarter of local residents, died in the three-month ground battle in Okinawa between Japanese and U.S. troops. Overall, more than 200,000 lives were lost, including those of Americans.