What to know about the investigation into a teen's death on a cruise ship

ORLANDO, Fla. — A 16-year-old boy who is under investigation in the death of his 18-year-old stepsister on a Carnival Cruise ship appeared in federal court in South Florida late last week, but the reasons have been obscured because of his age.

Unlike adults, juvenile cases are closed to the public, so there was no explanation why the teen was on the docket at the Miami courthouse or whether he's been charged with a crime. Juvenile cases aren't common in federal court and are often sent to state courts, or the juvenile is tried as an adult.

The death of the teen's stepsister, Anna Kepner, was ruled a homicide. Her death has drawn international attention and sparked intense speculation on social media. The Associated Press is not naming the teenager because of his age and because any charges that may exist have not been made public.

Here's what we know about the case.

Who was Anna Kepner?

Anna Kepner was a high school cheerleader at Temple Christian School in Titusville, Florida, some 40 miles (65 kilometers) east of Orlando on the state's Space Coast. Friends described her as someone who loved spending time on the water. At her memorial service in November, family members encouraged people to wear bright colors instead of the traditional black ''in honor of Anna's bright and beautiful soul.''

Kepner was part of a blended family after her father, Chris, married Shauntel Hudson, who had three children, including the 16-year-old boy, with ex-husband Thomas Hudson. Much of what is known about the investigation into Kepner's death, including that the stepbrother was a suspect, has come from court documents tied to a custody dispute between the exes.

Before the ship was scheduled to return to Florida, Kepner's body was found concealed under a bed in a room she was sharing with two other teens, including the younger stepbrother. The cause of death was determined to be mechanical asphyxia, which is when an object or physical force stops someone from breathing.

Why juvenile federal cases are so rare and secret

The 16-year-old boy was seen last Friday at the federal courthouse in Miami, wearing a ball cap and a camouflage hoodie pulled tightly around his face. Again, it's unknown if any charges have even been filed.

Juvenile cases in federal court are exceedingly rare. The only reason this case landed there was because Kepner died in international waters, said Fritz Scheller, a defense attorney in Orlando.

Scheller said Wednesday that in 27 years practicing law in federal court, he has never seen a juvenile case.

Secrecy is part of the juvenile justice system so that a child's mistakes won't haunt them for life, said Carla Barrett, an associate professor at the John Jay College of Criminal Justice, part of the City University of New York.

''The idea was, kids are malleable. They're worthy of some sort of attempt at rehabilitation,'' said Barrett, who wrote a book on juvenile justice, ''Courting Kids: Inside an Experimental Youth Court.''

The parents' statements

After the teen's court appearance, Anna Kepner's father Chris and stepmother Shauntel, the suspect's biological mother, issued a statement to ABC News in which they said they were disturbed ''that the person responsible is able to walk freely.''

''This reality adds to our grief and outrage,'' they said. "It is devastating to know that while we live every day with the loss of our child, the individual responsible has not yet been fully held accountable. This only strengthens our resolve to continue seeking justice for our daughter.''

Anna Kepner's biological mother, Heather Wright, said on social media that she hoped for a full resolution of the case.

''Pray for justice for my daughter,'' she said.