Anna Kepner, an 18-year-old Florida high school senior, was found dead on a Carnival cruise ship on 8 November, and investigators say she died from asphyxiation consistent with a bar hold.

Her grandparents told ABC News that authorities have identified Anna’s 16-year-old stepbrother as a suspect, though the FBI has not confirmed any details.

The stepbrother, who was on the cruise with the family, was reportedly hospitalized for psychiatric observation and has told relatives he does not remember what happened.

Family members described the blended family as close and said there had been no prior signs of conflict between Anna and her stepbrother, The Guardian has reported.

Though learning details of her death offers some clarity, the grandparents said it does little to ease the loss of both grandchildren they fear they have now lost.