Police in Costa Rica have discovered a woman's body "in a state of decomposition" near where a missing Florida woman was last seen.
Officials have not confirmed the identity of the remains, Walter Espinoza of Costa Rica's Judicial Investigation Department told reporters in the capital, San Jose.
The body was found around noon Monday in a wooded area of the San Jose neighborhood of San Antonio de Escazu, he said. Authorities are awaiting autopsy results, which they expect will be released Tuesday.
US citizen Carla Stefaniak, 36, was reported missing by her family in Florida last week. Relatives raised the alarm after she stopped texting and telephoning home and was not on her return flight from Costa Rica, where she had been vacationing.
Costa Rican authorities found stains inside the apartment where Stefaniak was staying, "which are compatible with blood and which will be submitted to further investigation and comparison," Espinoza said.
The last time anyone heard from Stefaniak was Wednesday night, according to April Burton, her sister-in-law.
Burton told CNN the two were in Costa Rica to celebrate Stefaniak's birthday, and had traveled together for six days.
Burton left the country Wednesday, and Stefaniak's flight back to Florida was scheduled for the next day.
The two texted each other via WhatsApp throughout the day Wednesday, Burton said, until Stefaniak suddenly stopped responding to her messages that evening.
And on Thursday, Stefaniak did not board her flight home.
"That's when we knew that something's not right," Burton said. "You never want to think the worst, but that's where your mind goes to automatically. We're going on six days not hearing from her. That's kind of where we are right now."
Burton added: "For almost six days to go by and no contact, she would have to have been abducted. She is very active on social media, and for her, on the day of her birthday, to never log in to any of those accounts, is just crazy."
A US State Department representative told CNN that officials are aware of the reports of a missing American in Costa Rica.
"When a US citizen is missing, we work closely with local authorities as they carry out their search efforts. We stand ready to provide all possible assistance to US citizens in need and to their families. Due to privacy considerations, we have no further comment," the representative said.
Speaking Monday to HLN, CNN's sister network, Burton urged anyone who might have information about her sister-in-law's whereabouts to come forward.
"She's a great person. So friendly, so bubbly, loves to travel, loves fashion, loves social media," she said.