Searches on land and by divers off the coast have turned up no sign of Yvonne Baldelli, 42, of Laguna Niguel, California, whose family reported her missing in January.
Panamanian police investigator Alexis Munoz told the AP that his officers, FBI agents and forensic specialists were using a chemical that could reveal signs of blood on the walls and floor of the hostel El Sapo, in the Bocas del Toro archipelago, a popular tourist spot where Baldelli was last seen on Nov. 26.
She was seen with an American boyfriend, who left for Costa Rica days later and has since returned to the U.S., according to Munoz.
Authorities said they were looking for signs that Baldelli may have been a victim of violence in the hotel. Baldelli and her partner stayed at the two-story hostel for about two months. Munoz said Baldelli's family had lost any contact with her at the end of November, "which makes us think that there may have been some crime against her."
The investigation indicates that Baldelli arrived in Panama accompanied by her partner, who left the country about 10 to 12 days after she was last seen, Munoz said.
Baldelli's family only reported her missing to Panamanian authorities in January.
Baldelli's sister, Michelle Faust, has said the boyfriend returned to the U.S. in December and family members had spoken with him, but she didn't offer details.
Faust and her family helped with the search Friday, along with a group of divers led by the FBI.
Faust called her sister a "great and talented" woman who had wanted to sell bathing suits to the thousands of tourists who flock to Bocas del Toro each year, many of them from the U.S.