-- The discovery of two American sisters dead in their hotel room turned the vacation of a lifetime in Africa into a heartbreaking tragedy.
The bodies of Robin Korkki, 42, of Chicago and Annie Korkki, 37, of Denver were discovered last week in the same hotel room of their luxury $2,000 a night resort in the Seychelles, off the coast of East Africa.
An autopsy determined the cause of death for both sisters as "acute pulmonary edema," a build up of fluid in the lungs. The autopsy determined that Annie also suffered a "cerebral edema," a swelling in the brain.
"When you are talking about pulmonary edema, that's a really big deal," said ABC News consultant and former FBI agent Brad Garrett said. "I would look primarily at drug use directly or indirectly by somebody else."
Their trip to the Seychelles, a chain of islands in the Indian Ocean known for its stunning beaches and resorts, was part of a nearly month-long African vacation.
Both sisters worked in banking. Robin's LinkedIn account showing she was a commodities trader, and younger sister Annie worked at JPMorgan Chase, according to her Facebook page.
The sisters were described as "loving sisters and best friends." They often shared details of their travels to exotic locations on social media, and Annie had posted photos on Facebook just days before the hotel announced the tragic discovery.
The sisters were discovered "when an employee of the hotel tried to wake them" in their villa, according to a statement from the hotel.
The day before their bodies were discovered, the pair had been seen drinking at the resort until about 6:45 p.m. and were later helped to their rooms by staff at 8:15 p.m., according to local news reports.
When the sisters were discovered the next morning, on Sept. 22, "no visible signs of injuries were found on the bodies," according to the police report.
"If this is a murder then it is somebody that gave them something," Garrett said. “Based on their apparent health and age, that it’s something that they ingested and/or inhaled that caused their death.”
Medications found in the sisters' room have reportedly been confiscated as part of the investigation, which will also include a toxicology analysis.
ABC News has confirmed the sisters' mother and brother have traveled to the Seychelles to bring home the bodies of Robin and Annie.