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A Florida woman on a birthday trip to Costa Rica vanished last week under what her family described as suspicious circumstances.

Carla Stefaniak, of Hallandale Beach, Florida, had traveled to the Central American country with her sister-in-law to celebrate Stefaniak’s 36th birthday, her brother, Mario Caicedo, said in an interview Sunday.

Stefaniak checked in for her Nov. 28 return flight at some point within 24 hours of its departure. But she never showed up to board the plane, he told NBC News.

“She had been ready to come back home but she didn’t,” Caicedo said. “That means somebody kidnapped her or abducted her.”

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Carla Stefaniak, 36, of Hallandale Beach, Florida. via Facebook

Caicedo said the Costa Rican law enforcement agency Organismo de Investigación Judicial is investigating Stefaniak’s disappearance. The agency did not immediately respond to a request seeking comment.

Caicedo said his family has also been touch with the United States embassy in Costa Rica. No one there could immediately be reached for comment.

Stefaniak planned on leaving the day after her sister-in-law’s flight, according to a timeline of Stefaniak’s final day in Costa Rica provided to NBC News. The timeline shows that Stefaniak dropped off her sister-in-law and rental car at the San Jose airport on Nov. 27 before touring the city with an Uber driver.

After Stefaniak returned to the Airbnb where she was staying that night, she posted a message on Whatsapp saying there were heavy rains. The Airbnb listing appears to have since been removed.

“Power went off,” she posted at the time, according to the timeline. “Super sketchy.”

During a FaceTime call with a friend, Stefaniak mentioned that she might ask a security guard at the Airbnb to buy her water because of the storm, the timeline says.

She was on WhatsApp at 8:20 p.m., then her phone died at 9 p.m., and she has not posted online since.

Stefaniak, who sells insurance in Hallandale Beach, north of Miami, is one of four siblings, Caicedo said. He described her as upbeat and social — the kind of person who would have been checking all of the birthday messages posted on social media.

“She never got back online to check all these birthday wishes,” he said. “This is one more thing telling us that she was abducted.”