Investigators searching for missing Japanese centenarians in a well-publicized nationwide hunt made a particularly grisly discovery this week when they reportedly found the remains of a 104-year-old Tokyo woman stuffed into her son's backpack.

The remains were found by police Thursday in an apartment in Tokyo's Ota ward, where the dead woman's 64-year-old son lived. He told police his mother had died in June 2001, but that he hadn't been able to afford a proper funeral or burial.

"I laid her body out for a while, washed it in the bath, then broke up the bones and put them into a backpack," the man said, according to reports. "Because I didn't have money for a funeral, I didn't report her death."

Authorities are now investigating the man on suspicion of criminal damage to a body and fraud charges, as he continued to collect his mother's pension. In addition, the local government is believed to have sent her about 150,000 yen ($1,800) to celebrate what was believed to be her longevity.

Japan has over 40,000 people registered as age 100 or older, roughly 87 percent of which are women. Police officials began the national search recently when nearly 200 of them were deemed missing, raising concerns that relatives were failing to report their deaths in order to continue to exploit the pension system.