The Federal Bureau of Investigation is now helping to probe the deaths of three Americans who perished under mysterious circumstances in a five-day span at neighboring resorts in the Dominican Republic, officials said Tuesday.
Dominican authorities asked for the FBI's help in conducting toxicology analysis in the investigations stemming from the deaths at the luxury destinations run by the Bahia Principe Hotels & Resorts, according to the U.S. Embassy in Santo Domingo.
"The safety of U.S. citizens that live in, work in, and visit the Dominican Republic remains our highest priority," Robin Bernstein, the U.S. Ambassador to the Dominican Republic, said in a statement. "These incidents are tragic and we offer our deepest condolences to those personally impacted."
FBI officials have informed Dominican authorities that getting results of the toxicology analysis could take up to 30 days.
"We ask everyone to be patient while these investigations run their course," a statement from the U.S. Embassy in the Dominican Republic reads.
News of the FBI's involvement came as the bodies of a Maryland couple found dead in their room at one of the resorts were returned to the United States and the families of both said they want independent autopsies conducted in hopes of getting to the bottom of how they perished, an attorney for the loved ones said.
The remains of Edward Nathaniel Holmes, 63, and Cynthia Ann Day, 49, arrived in Maryland on Tuesday morning, Steven E. Bullock, an attorney for the couple's families told ABC News.
Bullock said independent tests are expected to be run on the couple to shed new light on what killed them as they vacationed at the Grand Bahia Principe La Romana Resort in San Pedro de Macoris on the southeast coast of the Dominican Republic.
"We plan to do our own toxicology and autopsy," Bullock said.
Holmes and Day, who were engaged to be married, were found dead on May 30 in their room at the resort.
Autopsies performed in the Dominican Republic determined preliminary causes of death for both Holmes and Day were respiratory failure and pulmonary edema, or water in the lungs.
Authorities in the Dominican Republic have yet to determine what triggered the fatal symptoms in the couple at approximately the same time and are awaiting the results of toxicology and histopathology tests.
The couple died just five days after Miranda Schaupp-Werner, 41, of Allentown, Pennsylvania, was found dead at the Luxury Bahia Principe Bouganville hotel at the same resort.
An autopsy performed on Schaupp-Werner determined that she also died from respiratory failure and pulmonary edema, according to the Dominican Republic National Police.
Day, Holmes and Schaupp-Werner were all described by their families as healthy before they traveled to the Dominican Republic.
Authorities investigating the deaths have not commented on any common possibilities that could have led to the fatalities.
Both the Grand Bahia Principe La Romana and the Luxury Bahia Principe Bouganville are run by Bahia Principe Hotels & Resorts, which is a subsidiary of the Spanish company Grupo Pinero.
"Bahia Principe Hotels & Resorts would like to express our deep respect to the authorities and the ongoing investigations," the company said in a statement. "We reiterate our firm commitment to collaborating completely with the authorities and hope for a prompt resolution of their inquiries and actions."
The bodies of Holmes and Day showed no signs of violence when they were discovered, police said. Several bottles of medicine used to treat high blood pressure were found in the couple's room, according to authorities. No other drugs were found.
Schaupp-Werner died suddenly in her hotel room after having a drink from the in-room mini-bar, a family spokesperson, Jay McDonald, said in a statement to ABC News.
McDonald said Schaupp-Werner died on the day she arrived in the Dominican Republic with her husband, Daniel Werner.
An official at the U.S. Department of State said they are "actively monitoring" the investigations into the deaths of the three Americans.
"At this point, we are not aware of any connection between these incidents," the official told ABC News in a statement.
Meanwhile, Kaylynn Knull and her boyfriend, Tom Schwander, of Colorado, said they both became ill while staying at the Grand Bahia Principe hotel in June 2018.
Knull and Schwander told ABC Denver affiliate KMGH that they woke up in the room early one morning covered in sweat. They said they were also drooling excessively and their eyes would not stop watering.
They said that prior to becoming sick, they noticed a strange smell in their room, describing it as if someone "dumped paint everywhere."
After returning home, Knull and Schwander were examined by their doctor who told them they likely experienced poisoning from organophosphate, a form of insecticide, which Knull said she believes was being used on plants around the resort.
Knull and Schwander sued the Grand Bahia Principe La Romana after the resort refused to reveal the chemical used on its grounds or refund their money.
Resort officials did not respond to ABC News' request for comment on the couple's claims.
ABC News' Julia Jacobo contributed to this report.
FBI involved in probe of deaths of US citizens at Dominican Republic luxury resorts