Other staff members were dismissed for what appeared to be inappropriate behavior, the court said.
The ICC started an investigation in the DRC in June following reports that four individuals under its protection were abused sexually by a former staff member working in the country.
"[A] review panel confirmed the results of the ICC's initial internal inquiry and concluded that one person alone, the alleged perpetrator, would bear criminal responsibility for the alleged crimes if proven," the court said in a statement.
The court said it made the decision to start a third-party review after completing an internal audit.
It was also concluded that other staff members "likely" engaged in conduct in the DRC that was considered inappropriate.
"Disciplinary measures, including dismissal, have already been taken in respect of certain staff involved," the court said. "[Court authorities are] in the process of analyzing the content of the full report in order to assess whether further disciplinary action is required."