The police found the severed parts, including a torso, two arms and two legs, in three locations in northern Osaka Prefecture and Kyoto, on Sunday evening. She was reported missing on by her relatives on February 17, Japanese daily Asahi reported.
"I never heard of a trouble here, so I'm surprised", said a 73-year-old resident of the building where the head was found, which houses mostly seniors on welfare benefits.
The woman, 27, had apparently told friends she was going to see an American she had met on an app.
Bayraktar is seen leaving and re-entering the apartment with a large bag multiple times throughout the day in the camera footage.
Bayraktar was the last person to be seen with the missing woman before she disappeared.
They later found what appeared to be the woman's head inside a suitcase at a flat Mr Bayraktar had booked in Osaka through a private holiday rental site, local media said.
Security footage reportedly captured the pair meeting at a train station in Osaka around midnight and then entering the apartment building together. On Saturday, officers found what is believed to be the head of the woman inside a suitcase in a residence in Osaka's Nishinari Ward.More news: North willing to hold talks with US: South Korea
He has been identified by local media as Yevgeniy Vasilievich Bayraktar, 26, from NY, and reportedly entered Japan in January for a sightseeing trip. A severed head was reportedly discovered in Hokkaido late last week.
She was reported missing on February 17, two days after friends last heard from her.
The suspect, who arrived in Japan in January, was arrested Thursday on charges of confining the woman against her will.
Bayraktar, a USA national who entered Japan in late January, was the last person seen with the woman.
The suspect has allegedly denied any connection with the case.
Hyogo Prefecture police, where the unnamed missing woman is from, declined to answer questions Monday night.