Working on a tip, police last week arrested 26-year-old New Yorker Yevgeniy Vasilievich Bayraktar on suspicion of confining the woman, who had been reportedly missing since February 16, media said.
Law enforcement received a tip that Bayraktar was keeping a woman locked up in the apartment.
Security camera footage shows the woman boarding an Osaka-bound train alone at a nearby station. Sources cited by Kyodo said a large amount of air freshener had been used inside the apartment but no blood had been found.
On Feb. 24, law enforcement reportedly found the unidentified missing woman's severed head in a suitcase in the Osaka apartment - reportedly one of multiple condos the American rented while visiting Japan. The arms and legs looked like they were severed with a sharp knife, Tokyo Reporter said.
Reports indicate Bayraktar has refused to answer questions from investigators, but has denied the accusations against him.More news: Frank Lampard Criticises Jonjo Shelvey's Defensive Efforts in Draw Against Bournemouth
The prefectural police believe all the newly found body parts are those of the missing woman and are working to confirm the body's identity. They are believed to belong to the Hyogo woman.
According to the announcement, a naked torso and two arms were found on a mountain behind residential areas in Shimamoto, Osaka Prefecture, and the legs were found in a wooded area in Yamashina Ward, Kyoto. None of the woman's belongings have been found.
The arrest comes four months after Japan was transfixed by another grisly case, in which the dismembered bodies of nine people were found in coolers and other containers, in some cases covered in cat litter. It said he had been in contact with several women through dating apps, through which he met the 27-year-old woman.
The Washington Post said the woman had told friends she was "going to see an American for a date" and told Instagram followers in a February 15 posting she was off to "meet Jay".