John Minchillo / AP

Betzaida Jimenez, mother of 33-year-old Sarai Sierra who was found dead on Saturday in Turkey, pauses before a news conference at a friend's home in Staten Island, on Monday.

The FBI is playing a significant role in the investigation into the death of a New York City woman in Istanbul while on a solo vacation, a U.S. congressman said Monday.

Rep. Michael Grimm, a former FBI agent, said U.S. investigators were invited by Turkish authorities to assist as they try to find out what happened to Sarai Sierra, a 33-year-old mother of two who disappeared Jan. 21. Her body was found 12 days later, near the remnants of the city's ancient walls. Police said she had suffered a fatal blow to the head.

Prosecutors in Istanbul got a court order Monday for authorities to take blood and DNA samples from 21 people already questioned in the death, according to Turkish state media.

Meanwhile, her family was working out how to return her body to the U.S.

Sierra's husband, Steven, is in Istanbul, where he traveled last week to help in the search. He intends to accompany her body back to New York, but the family is still determining how to fund the transport. Their church and friends are working to raise money to help defray the costs.

Turkish authorities finished an autopsy Monday on Sierra and gave DNA samples from it to a crime lab, the state-run Anadolu Agency reported. After that, Istanbul prosecutors got the court order but did not identify the possible suspects, the agency reported.

On Monday, police with sniffer dogs were scouring the area where the body was found for clues, it said. The Milliyet newspaper said the forensic lab will examine samples from Sierra's fingernails as well as hair and other samples from a blanket found near her body. It said some nail scrapings suggest she may have tried to fight off at least one attacker.

Sarai Sierra made her first trip overseas alone after her childhood friend, Magdalena Rodriguez, backed out. At Monday's news conference in New York, Rodriguez fought back tears as she said she wished she had not changed her plans.

"I wasn't working at the time and I didn't have the money to go," she explained.

Family and friends described Sierra as a devoted mother to her 9- and 11-year-old sons who volunteered at their school and worked part time so she would be available for them after school. "Every time I saw her, she was always with her family," said another longtime friend, Dulce Arroyo.

Arroyo ran across Sierra on a shopping trip two days before she left the U.S. and said traveling alone didn't appear to be a frightening prospect. Her friend was looking forward to an exciting adventure and spent most of their conversation talking about the murals and architecture she planned to photograph.

"She was perfectly OK with taking this trip on her own," Arroyo added. "She was thrilled."

Dennis Jimenez said Sierra tried to calm any fears by emphasizing that she'd be in regular contact via video calls and text messages.

"I didn't want her to go, but she wanted to go," he said. "Turkey was a land rich in architecture and ancient history, and she was very fascinated by that."

He added that she shared her photos online and checked in frequently. "You could tell that she was happy," he said.

Grimm said Turkish police still have hours of video footage to review as they piece together Sierra's last movements. A special unit of Turkish police set up to find Sierra have an image of her at Galata Bridge, which spans Istanbul's Golden Horn waterway and where she went on her last day to take photos.

The trip also included preplanned excursions to Amsterdam and Munich.

Betzaida Jimenez said her two grandsons do not know what had happened to their mother. They only know their father went to get her after her vacation.

"We're going to talk about that when he gets back," she said.

She recalled hugging her daughter before she departed and praying together for a safe journey.

"Just the thought that I'll never be able to hug her again," she said, pausing to compose herself. "We just didn't think a tragedy like this was going to happen."

Related: Mom of woman slain in Turkey: Her sons don't know

AP

Turkish men pin up a photo of Sarai Sierra, a New York City woman who disappeared while on vacation in Istanbul.

The cellphone of a New York City mom missing in Istanbul has been used twice since she vanished, a Turkish newspaper reported Friday.

Sarai Sierra, 33, hasn’t been seen heard from since Jan. 21, the day before she was supposed to catch a flight home from a two-week vacation.

But police believe the amateur photographer is alive because her phone was used for a Skype call on Wednesday and turned on again Thursday, the Sabah newspaper reported, according to the Turkish daily Hurriyet.

Cops briefly detained a man who exchanged online messages with Sierra after meeting her online four months ago, contacted her while she was in Istanbul and made plans to rendezvous with her on a bridge she wanted to photograph, Hurriyet said.

The man reportedly told police the two never connected, and investigators are now hoping to question three other people she corresponded with on Facebook and Twitter.

Sierra left for her first trip abroad on Jan. 7 — flying solo after a close friend dropped out of the prepaid trip, her family has said.

Her husband, Steven Sierra, said his wife stayed in close contact, talking to him and their children, ages 9 and 11, by phone and Skype.

The last communication from her came Jan. 21, when she sent her sister a brief message saying she would be home the next day.

When she didn't show up at the airport, her husband called her hostel, which said her passport and other personal items were still there.

Police uncovered surveillance-camera footage of Sierra walking around Istanbul during her visit; she appeared to be alone and well.

Steven Sierra and Sarai's brother, David Jimenez, flew to Turkey earlier this week and turned over her online communications to police.

"I don't want to come home without my sister," Jimenez told NBC New York before the trip.