A United States Marine has been taken into custody for questioning after a 14-year-old girl who was reported missing was found at Marine Corps Base Camp Pendleton in San Diego County, California, last month, authorities said.

The girl was reported missing by her grandmother on June 13, according to the San Diego County Sheriff's Department.

On June 28, she was discovered in the barracks at Camp Pendleton. A Marine with Combat Logistics Battalion 5, 1st Marine Logistics Group has since been taken into custody for questioning by Naval Criminal Investigative Services, 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 said in a statement Sunday to CNN.

NCIS declined CNN's request for comment "out of respect for the investigative process."

Detectives interviewed the teen, the family was offered services and she has been returned to her grandmother, according to the sheriff's department.