OSAKA — The man arrested in Friday's fatal stabbing of eight children at an elementary school in Osaka Prefecture made a huge number of prank calls to his former wife, his former adoptive mother and a man in Hyogo Prefecture, police sources revealed Tuesday.

Mamoru Takuma, 37, began making the calls almost daily starting around May 1999 through mid-May this year, sometimes more than 10 a day, the sources said.

He called late at night, saying "I'll kill you," "I will take your life by .22 caliber," or "I won't be held responsible for anything I do because I have a mental illness," the sources said, adding he had made more than 1,000 calls a year.