(CNN) Authorities have so far uncovered nothing to suggest that two Saudi Arabian sisters whose bodies were found bound on the banks of the Hudson River were victims of foul play, according to a law enforcement official who spoke to CNN on the condition of anonymity.

The case remains steeped in mystery more than a week after the bodies of 22-year-old Rotana Farea and 16-year-old Tala Farea of Fairfax, Virginia, were discovered in upper Manhattan with their feet and waists bound together by duct tape.

Water was found in the sisters' lungs, the official said, leading investigators to believe they were alive when they entered the water. Police previously said the bodies showed no signs of trauma.

New York Police Department investigators believe the deaths to be suicides, the official said, though detectives are still investigating the circumstances surrounding them.

Still, the NYPD is not ready to officially determine the causes of death. According to NYPD deputy commissioner of public information Phil Walzak, authorities are still actively investigating whether the deaths were the result of suicide, homicide or an accident.

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