The 16-year-old possibly suspected in his stepsister's death aboard a cruise ship was “an emotional mess” when her body was found, according to family members.

Anna Kepner, an 18-year-old high-school cheerleader from Titusville, Fla., was on a family vacation when she was found dead under a bed on a Carnival Horizon cruise ship on Nov. 8.

The FBI is investigating the case, the agency previously confirmed to PEOPLE. Officials have not publicly named a suspect or a person of interest.

Court filings unrelated to the case, however, claim Anna's 16-year-old stepbrother may be a “suspect” in her death.

In a petition filed in a child custody case, Thomas Hudson, the biological father of Anna's 16-year-old stepbrother said the teen is a “suspect in the death of the step child during the cruise,” according to a court document obtained by PEOPLE.

Hudson's ex-wife, Shauntel Hudson, who is the 16-year-old boy's biological mother and Kepner's stepmother, also made similar statements, claiming the FBI informed her that her son could be facing a criminal case following Kepner's death, according to a court document obtained by PEOPLE. (Shauntel's last name is listed as “Kepner” in several media reports, but court documents identify her as Shauntel Hudson.)

Kepner's grandparents said in a recent interview that the teen and her stepbrother were very close — like “two peas in a pod.”

After Kepner's body was found, the stepbrother was seemingly aghast, her grandmother Barbara Kepner told ABC News in an exclusive interview.

“He was an emotional mess. He couldn't even speak,” Barbara said in the interview. “He couldn't believe what had happened.”

Security footage shows that the boy, who was sharing a room with Kepner, was the only person seen going in and out of the room, investigators told the family, per Barbara.

He allegedly said he had no recollection of what happened.

“In his own words, say he does not remember what happened,” Barbara told ABC News. “I believe, to him, that is his truth.”

She declined to comment on speculation about a criminal case against him.

“I can't accuse him because I don't know what happened in that room,” she said.

The teen was hospitalized for psychiatric observation after the cruise ship reached Miami, Barbara added, confirming previous statements by Hudson's lawyer. He has since been released.

Information about the circumstances surrounding Anna's death and the ensuing investigation remains limited two weeks on, as officials continue to be tight-lipped about the case.

A formal ruling regarding the cause and nature of her death has not been publicly announced. A source close to the investigation previously told ABC News Kepner died by asphyxiation from a “bar hold” — meaning an arm held across the neck.

PEOPLE has not independently verified this information, and was redirected to the FBI upon previously contacting the medical examiner's office.

PEOPLE has reached out to the FBI for further comment.