The father of Anna Kepner is speaking out about his 16-year-old stepson, who, according to court documents in an unrelated custody matter, is possibly under investigation in connection with Anna’s death.

Christopher Kepner, 41, says he last saw his 18-year-old daughter on the evening of Nov. 6 when the family gathered for dinner aboard the Carnival Horizon.

Anna’s body was found under a bed the following day by a housekeeper, Christopher tells PEOPLE. Anna’s death certificate, which was obtained by PEOPLE, says she was “mechanically asphyxiated by other person(s).”

Soon after the FBI began investigating the case, Christopher’s wife, who is Anna’s stepmother, said in unrelated court filings that her 16-year-old son may be subject to a criminal investigation.

The FBI has not publicly announced a suspect or person of interest in the case.

While declining to confirm or deny any knowledge about his stepson’s possible involvement, Christopher tells PEOPLE, “I do not stand behind what my stepson has done.”

He adds: “I want him to face the consequences … I will be fighting to make sure that does happen.”

When asked whether he believes his stepson is responsible for Anna’s death, Christopher says, “I cannot say that he is responsible but I can’t decline. He was the only one that was in the room and the FBI has an ongoing investigation in which they will have to provide the evidence to say that he did do it or did not do this.”

Anna Kepner.

Anna Kepner.Anna Kepner/Instagram

“He was a normal kid,” Christopher says, echoing similar sentiments shared by Anna’s grandparents in a previous interview with ABC News.

“And I would’ve never thought that any of this would’ve happened,” he adds.

Anna’s grandmother Barbara Kepner told the outlet that the slain teen and her stepbrother were close.

“They were just like brother and sister,” Barbara told ABC News, adding that they were “two peas in a pod.”

Authorities have not discussed details of the investigation. The FBI previously confirmed with PEOPLE it is investigating the case, but it has declined to comment further.

Christopher tells PEOPLE, “Right now, my best course of action is to let the FBI do what they’re doing.”

He adds, “They have the evidence that they need. When they make the arrest then we’ll start seeing the justice side of things.”