A U.S. Marine was detained last month after a missing 14-year-old girl was found in the barracks of Marine Corps Base Camp Pendleton in California, authorities said. The girl’s grandmother reported her missing on June 13, per the San Diego County Sheriff’s Department. It wasn’t until June 28 that she was found at Camp Pendleton. An unidentified Marine has been in custody ever since, according to Capt. Charles Palmer spokesperson for 1st Marine Logistics Group. “This command takes this matter and all allegations very seriously. The incident is under investigation, and we will continue to cooperate with NCIS (Naval Criminal Investigative Services) and appropriate authorities,” Palmer told CNN on Sunday. The San Diego Human Trafficking Task Force is also investigating the incident. The relationship between the Marine and the missing girl remains unclear, as does how she ended up at Camp Pendleton.