By KATE PAYNE and JEFF MARTIN, Associated Press

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.

Kepner’s time of death was 11:17 a.m. on Nov. 7, according to the medical examiner’s office. The ship returned to PortMiami on Nov. 8 as scheduled.

Carnival Horizon cruises the Western Caribbean with stops in Cozumel, Grand Cayman, Montego Bay and Ocho Rios, according to itineraries posted on the company’s website.

Nelson, the medical examiner, said he considers Kepner’s death “highly, highly suspicious” and said the reports that her body was concealed support the homicide finding.

“The concealment part alone is very troubling,” Nelson said, adding, “If (drug screenings) are clean and she’s not overdosed, then you know it would be clearly a homicide.”

Kepner’s family has been told that preliminary information indicates there were no signs of sexual assault and that there did not appear to be drugs or alcohol in Anna’s system, ABC News reported.

Nelson, who has not been briefed on the case, said there are a range of deaths that can be defined as asphyxia, including drowning, strangulation and hanging.

The language stating that Kepner “was mechanically asphyxiated by other person(s)” is fairly standard language, Nelson said, and an acknowledgment that Kepner had been sharing a room with other people.

“It would be up to law enforcement to narrow down what role, if any, each of those other people in the room played,” Nelson said.

Determining who has the authority over a criminal investigation can be complicated since cruise ships are registered in one country but often travel through many others, all while carrying thousands of passengers and crew members from around the world, the FBI said in a document that outlines the challenges of investigating crimes on cruise ships.

On the high seas where U.S. law, international law and the laws of other nations might be involved, cooperation is critical to any investigation, the agency says.

The nature of a floating crime scene can also make investigations challenging because it can leave a small window of time to investigate before the ship departs on its next voyage.

“You have a short amount of time to do the best you can to solve this case or collect all the evidence you need to solve this case and then your crime scene leaves,” FBI Special Agent Matt Parker said in the FBI document.