A 16-year-old boy in Florida has been charged with murder and aggravated sexual abuse in the death of his 18-year-old stepsister aboard a Carnival Cruise ship.

The victim, Anna Kepner, was found hidden under a bed in their shared cabin after the ship returned from a November voyage.

Authorities say the cause of death was mechanical asphyxia, and prosecutors allege serious federal crimes occurred in international waters.

The suspect, Timothy Hudson, was initially charged in February and has since been indicted and will be prosecuted as an adult, the AP has reported.

The case has deeply affected the victim’s family and is now proceeding through federal court.