(MIAMI) -- A 16-year-old boy charged as an adult with first-degree murder and aggravated sexual abuse in the death of his stepsister during a family cruise has pleaded not guilty, court records show.

The teenager was due in court in Miami on Wednesday morning for his arraignment, though he waived his appearance, according to a filing from his attorney.

The Department of Justice announced the charges last week, months after 18-year-old Anna Kepner died in November on the Carnival Cruise ship Horizon while the ship was en route to Miami.

Prosecutors alleged that the stepbrother "sexually assaulted and intentionally killed" Kepner. The Florida high school senior died from mechanical asphyxiation, officials said. 

Anna Kepner's father, Chris Kepner, is married to the suspect's mother, Shauntel Kepner.

Chris and Shauntel Kepner said in a statement last week, "Our family is devastated by the loss of Anna and continues to grieve this unimaginable tragedy."

"This situation is deeply painful and complex for our entire family," the Kepners said. "Anna was deeply loved, and we remain committed to honoring her life and memory every day." 

ABC News' Sasha Pezenik contributed to this report.

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