Turkish police now say the victim, Sarai Sierra, had suffered a fatal blow to the head.
Istanbul police chief Huseyin Capkin said Sunday that forensic experts had not concluded their autopsy report, but that it was "clear" the head injury caused her death.
There is no evidence of rape, and she was found wearing the same clothes she had on the day she disappeared.
There is also no evidence of drugs, or that she was involved in any kind of trafficking.
Sierra's family remains in Turkey, searching for answers to her brutal murder.
Her husband, Steven Sierra, had the grim task of identifying her body.
Her children will not be told of her death until he returns to the United States.
NTV, a Turkish broadcaster, says 15 people have been detained for questioning in the case.
Sierra, a 33-year-old mother of two, was last heard from on Jan. 21, the day she was to fly home. Her disappearance attracted a lot of interest in Turkey, where the disappearance of tourists is rare, and Istanbul police had set up a special unit to find her.
The state-run Anadolu Agency said the body of a woman was discovered Saturday evening near the remnants of ancient city walls and that police later identified it as Sierra's.
The agency said she was found with a head wound and a blanket near her body. She was wearing jeans, a jumper and a jacket, and still had her earrings and a bracelet.
Sierra, whose children are 9 and 11, had left for Istanbul on Jan. 7 to explore her photography hobby and made a side trip to Amsterdam, Netherlands, and Munich, Germany. She had originally planned to travel with a friend, but ended up traveling alone when her friend canceled.
She was in regular contact with friends and relatives, and was last in touch with her family on Jan. 21, the day she was due back in New York. She told them she would visit Galata Bridge, which spans Istanbul's Golden Horn waterway, to take photos.
The body was found not far from the bridge and near a major road that runs alongside the sea of Marmara. Here tourists often photograph dozens of tankers waiting to access the Bosporus strait.
On Saturday, police stopped traffic there as forensic police inspected the area.
Anadolu suggested Sierra may have been killed at another location and that her body may have been brought to the site to be hidden there.
It was not clear if a Turkish man Sierra had exchanged emails with during her stay in Istanbul was among those being questioned. He was detained for questioning Friday, then released. Turkish news reports said Sierra had arranged to meet the man on Galata Bridge, but he reportedly told police the meeting never took place.
Shortly after her body was discovered, a woman came forward and told police she had seen a white car parked near the city walls as she was driving there the night of Jan. 29, Anadolu reported. She said a man was trying to remove "something" from the car.
"At that moment, I noticed a woman's hand," Anadolu quoted the woman as telling reporters after talking with police. The agency said she declined to give her name.
Sierra's husband, Steven, and her brother, David Jimenez, traveled to Istanbul to help search for her. Sierra's mother, Betzaida Jimenez, said Saturday that she couldn't talk about the case when reached in New York.
Shortly after Sierra was reported missing, Turkey set up a special police unit which scanned hours of security camera footage in downtown Istanbul in search of clues. A Turkish missing persons association joined the search, handing out flyers with photos of Sierra and urging anyone with information to call police.
While break-ins and petty thievery are common in Istanbul, the vast and crowded city is considered relatively safe compared to other major urban centers. Sierra's death was unlikely to have a significant impact on tourism, a large component of the Turkish economy.
In 2008, an Italian artist, Pippa Bacca, was raped and killed while hitchhiking to Israel wearing a wedding dress to plead for peace. Her naked body was found in a forest in northwest Turkey. A Turkish man was sentenced to life in prison for the attack.
CLICK HERE to see pictures from Istanbul, where Sierra's body was found.
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