Anna Kepner Murder

Anna Kepner was murdered on a Carnival Cruise ship ... at least that's the conclusion reached on her death certificate.

The document, obtained by ABC News, says Anna died as a result of "mechanical asphyxia" on November 6, and it notes the 18-year-old "was mechanically asphyxiated by other person(s)."

As you know ... FBI agents found two bruises on the side of Anna's neck, and she was thought to have died from a "bar hold" -- an arm placed across the neck.

Anna Kepner’s grandparents are shutting down any talk she was scared of her stepbrother -- the teen reportedly under investigation in her cruise-ship death -- making it clear they have faith in his innocence.

In an ABC News sit-down interview, Barbara and Jeffrey Kepner said 18-year-old Anna and her 16-year-old stepbrother were "two peas in a pod," and cared for each other "in the right way" -- a far cry from what Joshua Tew, Anna’s first love, claimed ... saying her other brother told him about a nasty blowout the pair allegedly had inside the cabin they were all sharing.

The grandparents say authorities told them the stepbrother is considered a suspect in the case. They admit they’ve got no clue what actually went down inside that cabin -- they’re waiting on answers just like everyone else -- but pointing the finger at the stepbrother? They’re nowhere near ready to go there.

Anna Kepner's ex has come forward with harrowing new details about the final moments of her life ... alleging she was involved in a heated confrontation with her 16-year-old stepbrother before her death.

Joshua Tew -- who described Anna as his first love during a new interview with Inside Edition -- said her 14-year-old brother Connor told him about a nasty fight she was allegedly in with her stepsibling in the cabin they all were sharing aboard Carnival's Horizon ship.

Anna and the unnamed brother were allegedly inside the locked cabin ... and according to Joshua, Connor could hear him "yelling at her in a harmful way." Joshua was told the stepsibling even yelled at her to "shut the hell up." There was also some "banging around" heard in the room ... including what the brother believes were chairs being thrown.

Anna Kepner -- the teen who tragically died on the Carnival Horizon earlier this month -- died from asphyxiation caused by a "bar hold" after someone’s arm was placed across her neck, according to a new report.

A source close to the investigation tells ABC News FBI agents found two bruises on the side of Anna’s neck after she was choked by an unidentified person ... The source also said preliminary information indicates there were no signs of sexual assault and no drugs or alcohol in the 18-year-old’s system.

The Miami-Dade County Medical Examiner is still working to determine a cause of death.

Anna Kepner was mysteriously found dead on a Carnival Cruise ship two weeks ago -- and we're now learning her stepbrother allegedly had a strange infatuation with the teen cheerleader ... even climbing on top of her in bed one time, according to a new report.

"Inside Edition" interviewed Steven Westin -- the father of Kepner's ex-boyfriend -- for an episode that aired Thursday ... and Westin made several shocking claims based on discussions he says he had with his 18-year-old son about Kepner's stepbrother.

As you know, Kepner, also 18, was on the Carnival Cruise with her stepbrother and other family members returning to Miami on November 7 ... when she was tragically found dead on board.

4:49 PM PT -- A spokesperson for Carnival Cruise Line tells TMZ ... "The Carnival Radiance crew responded to a potential overboard alert off the coast north of Ensenada, Mexico when some guests reported hearing a splash in the water.  The ship returned to the area where there was a potential sighting of an individual to conduct a rescue operation. In the meantime, the crew completed a full guest and crew headcount as is our standard safety protocol and all guests and crew have been accounted for. The splash could have very well been a whale but there is no way to confirm that. In any case, all on board are accounted for and the ship will resume its itinerary."

A rescue operation is underway in the Pacific Ocean after a passenger went overboard on a Carnival cruise.

Carnival Cruise Line tells TMZ ... the Carnival Radiance crew is responding to an overboard alert off the coast north of Ensenada, Mexico.

We're told the cruise ship is returning to where there was a potential sighting of a person in the water ... and we obtained video of rescue boats in the water searching for the passenger, plus footage of someone splashing around.

Anna Kepner's family is remembering the teen cheerleader as a radiant soul who "lived every day with her whole heart," following the tragic discovery of her body on a Carnival cruise ship.

Anna -- nicknamed "Anna Banana" -- was reportedly found by a maid wrapped in a blanket and hidden under a bed on November 8 during a Caribbean cruise with her father, Christopher Kepner, her stepmother Shauntel Hudson, and Hudson's kids.

Despite the tragedy, Anna's family focused their tribute on her joyful, light-filled life. "She loved the sun, the water, boat days, island days, and beach days, anything that let her soak in the light she so easily radiated to others," her obituary reads.

Federal authorities are continuing their investigation into the sudden death of 18-year-old Anna Kepner aboard a Carnival cruise ship -- and now they're zeroing in on a minor for possible criminal charges, according to a new filing.

The new development comes after Kepner's stepmom, Shauntel Hudson, recently filed a request to delay her court hearing in a custody case unrelated to the FBI probe into Anna's death, according to court documents.

In the family court filing ... Hudson states she's been informed by FBI investigators and her attorneys that a "criminal case may be initiated against one of the minor children of this instant action."

The passenger reported dead aboard a Carnival Cruise Line ship Saturday has reportedly been identified by her family as 18-year-old Anna Kepner, from Titusville, Florida.

The family told ABC News they will remember Anna as a "happy, bubbly, straight-A student with a bright future ahead."

The FBI is investigating the mysterious death of the young woman, who was set to graduate from high school in May, according to ABC. The death was reported as the ship was returning to Miami, Florida from a trip through the Caribbean.