A stepsibling of 18-year-old Anna Kepner is being investigated for possible involvement in the Florida teen’s death on a Carnival cruise ship earlier this month, a law enforcement source and a person familiar with the matter told CBS News. 

Kepner’s family believes her 16-year-old stepbrother is a suspect in an FBI investigation, according to court filings from a custody hearing obtained by CBS News. The court filings refer to the stepbrother as “T.H.”

“There is an open investigation regarding [Kepner’s] death… and T.H. is a suspect regarding this death which occurred recently on a cruise ship,” according to a filing Kepner’s stepmother, Shauntel Hudson, entered in the circuit court of Brevard County, Florida, on  Nov. 18. 

The filing came in response to one entered by Hudson’s ex-husband a day earlier amidst their custody dispute of their children, which also asserted the 16-year-old is a suspect. 

The FBI has not named anyone as a suspect in this case, and in a statement, the FBI said it does not provide operational updates on its investigations except in rare circumstances.

One law enforcement source said the two stepsiblings may have had some kind of altercation.

Kepner was on a family vacation in the Caribbean with her father, stepmother and three stepsiblings when she was discovered dead on the Carnival Horizon as it was headed back to Miami, where it docked on Nov. 8. Her body was found by a housekeeper under the bed in her stateroom, law enforcement sources told CBS News.

Kepner was staying in the same room as her stepbrother and one other stepsibling.

CBS News has confirmed the time of death listed by the medical examiner is 11:17 a.m. on Nov. 7; a source familiar with the investigation says this is around the time Kepner’s body was discovered.

According to family members, Kepner had told them the night before that she wasn’t feeling well and returned to her room. When she didn’t show up for breakfast the next morning, a frantic search began.

CBS News reported Tuesday that an unrelated court filing suggested charges may be coming against one of Kepner’s stepsiblings. That disclosure appeared in a motion made by Kepner’s stepmother, Shauntel Hudson, to reschedule a divorce hearing due to the matter.

“An extremely sensitive and severe circumstance has arisen wherein the Respondent/Mother will not be able to testify at the hearing at this time,” the filing stated.

CBS News has reached out to Hudson and her attorneys.

Investigators are now reviewing surveillance video from the ship and analyzing electronic swipe card data that may show who entered the teen’s cabin, the law enforcement sources said. They are also examining Kepner’s cellphone records. The FBI and ship security are also conducting interviews with other passengers, crewmembers and Kepner’s family.

In a statement, Carnival Cruise Line said it is cooperating with the federal investigation. The FBI has jurisdiction because Kepner is a U.S. citizen and the death occurred in international waters. The Miami FBI office is working closely with Carnival security.

Carnival also said the FBI has told it there is no related threat to safety aboard the ship on its current voyage.