Anna Kepner, an 18-year-old from Florida, was found dead aboard the Carnival Horizon cruise ship on Nov. 8, under a bed wrapped in a blanket and covered with life vests.

The cause of death has not been determined.

Investigators are examining possible causes, including an altercation with her stepbrother, a medical emergency, or an overdose, and are reviewing security footage and access records.

A court filing notes that her stepsibling could face charges, ABC News has reported.

The FBI is investigating, and Carnival Cruise Line is cooperating with authorities while supporting the family.