WASHINGTON, Nov 26, (AP): The death of a Florida teenager on a Carnival cruise ship earlier this month has been ruled a homicide, the latest development in a case that has drawn international attention and sparked intense speculation on social media. Anna Kepner's cause of death was "mechanical asphyxia," according to a copy of her death certificate obtained by ABC News, which said the 18-year-old "was mechanically asphyxiated by other person(s)."

Mechanical asphyxia is when an object or physical force stops someone from breathing, according to Stephen Nelson, a chief medical examiner in Central Florida who is not involved in the case. "In some way, shape or form, your airway has been cut off,” said Nelson, a former chair of Florida's Medical Examiners Commission.

A high school cheerleader from Florida’s Space Coast who was set to graduate next year, Kepner had been traveling on the Carnival Horizon ship with her father, stepmother, her stepmother’s two children and her grandparents. The night before she was found dead, Kepner had spent time with her grandparents in the ship’s casino, her grandmother Barbara Kepner told ABC News.

"She said, ‘Meemaw, I love you guys. I’ll see you. ... I’ll see you later’,” Barbara Kepner recalled. "We never saw her again after that.” The next morning, a medical alert blared out over the ship's broadcast system, directing first responders to the room Kepner was sharing with two other teens, including a younger stepbrother. A room attendant found Kepner's body "concealed under the bed," according to her grandmother.

"I just screamed. I couldn’t stop screaming,” Barbara Kepner said. Kepner's death aboard the ship that sailed from Miami has remained shrouded in mystery with the FBI and medical examiner’s office in South Florida refusing to disclose any information about the case for weeks. The teen’s 16-year-old stepbrother has been identified as a suspect in her death, according to court documents filed by his parents.

The disclosures - contained in motions filed in an ongoing custody dispute - offer the clearest public indication that federal investigators are scrutinizing a member of the victim’s own blended family. As of Tuesday, a final autopsy report had not been released and the Miami-Dade County Medical Examiner’s Office has not responded to recent messages left by the AP.