A 51-year-old man was arrested Sunday on suspicion of removing ashes from a grave in the city of Utsunomiya.
The ashes are those of the son of a woman he had been dating, local police said.
The suspect, with no fixed address, was identified as Norio Horikawa.
Police suspect Horikawa stole the ashes sometime between mid-November and Jan. 13.
According to investigations, Horikawa had been dating the woman from about two years ago. The couple had a difficult breakup, however, and Horikawa was quoted as telling police that he stole the ashes in the hope that it would give him an opportunity to contact the woman.
Horikawa had called the woman on several occasions threatening to steal the ashes if she did not agree to meet him, police said. He was found Sunday in Utsunomiya, and the urn containing the ashes was found in the back seat of his car, they added.