A 16-year-old Florida boy has been charged as an adult with murdering his 18-year-old stepsister Anna Kepner aboard a Carnival Horizon cruise ship in November. The teen, identified only as T.H. in court documents, allegedly sexually assaulted and killed Kepner while the ship was in international waters en route to Miami.

Federal prosecutors moved to charge the stepbrother as an adult after initially filing juvenile charges. Medical examiners determined Kepner died of mechanical asphyxiation in the cabin she shared with her stepbrother and a half-sibling. The case drew national attention due to the brutal nature of the crime and the jurisdictional complexities of prosecuting crimes committed in international waters.

Prosecutors argued the teen should be held in federal custody, describing the crimes as "the most serious, egregious and violative" acts one person can inflict on another. The indictment unsealed Friday charges him with first-degree murder and aggravated sexual abuse, both carrying potential life sentences. Carnival Cruise Line stated it was grateful for the FBI's investigation and praised its security teams' support.