The stepbrother of 18-year-old Anna Kepner, who was found dead on a Carnival Cruise ship in November, is being charged with first-degree murder, according to her mother.

Kepner’s body was discovered under a bed in the cabin she shared with her stepbrother and another sibling, and her death was ruled a homicide by mechanical asphyxiation.

The 16-year-old suspect was arrested, appeared before a federal magistrate on Feb. 6, and was released into the custody of a guardian.

The FBI is investigating the case, though no additional details about suspects have been released, the USA Today has reported.

Court records indicate the stepbrother was involved in family custody disputes and has been living with relatives while receiving therapy.