A Marine with Headquarters Battalion, 1st Marine Division, was arrested Monday for allegedly attempting to smuggle unauthorized immigrants across the U.S.-Mexico border, the Marine Corps announced.

The junior-enlisted Marine was arrested around 1:30 a.m. Monday by U.S. Customs and Border Protection personnel at the San Ysidro port of entry just south of San Diego, Marine spokesman 1st Lt. Cameron Edinburgh said in a Tuesday afternoon press release.

The 20-year-old Marine was driving a white 2007 Mustang through the port of entry when he was pulled aside for a more intensive inspection, a CBP spokesperson told Marine Corps Times in an email Tuesday night.

When officers opened the car’s trunk they found two women hiding inside who they identified as Chinese nationals with no legal authorization to enter the U.S., the spokesperson said.

The Marine is still in civilian custody while federal law enforcement and the military determine who has the adjudicating authority, but the Naval Criminal Investigative Service is investigating the incident, the press release said.

“We will continue to cooperate with civilian authorities on this case going forward,” Edinburgh said in the press release.

The incident is at least the second time this year Marines were arrested in connection to alleged human smuggling.

In early July Border Patrol agents arrested two Marines, Lance Cpl. Byron Darnell Law II and Lance Cpl. David Javier Salazar-Quintero, about seven miles from the border with three undocumented immigrants in the back seat, Marine Corps Times previously reported.

The subsequent NCIS investigation into the July 3 incident led to a mass arrest of 16 Marines with 1st Battalion, 5th Marines, in Camp Pendleton, California, at a battalion formation filmed by the Marine Corps.

Ultimately 13 Marines ― 10 arrested at the formation ― were charged with various allegations, ranging from the theft of smoke grenades to LSD distribution, all related to an alleged smuggling ring.

When the first hearings for the 13 Marines charged began in November, a military judge found the mass arrest violated the rights of the Marines accused, putting the Corps’ case against the 10 Marines arrested in formation in jeopardy.

At one of the initial hearings the lead NCIS investigator testified that there was no evidence the Marines actually smuggled anyone across the U.S.-Mexico border, but were rather accused of transporting unauthorized immigrant within San Diego County, California, the San Diego Union-Tribune reported.

The most recent arrest does not appear to have any connection to the Marines arrested during the summer, Edinburgh told Marine Corps Times in a phone call Tuesday afternoon.

This story is breaking and will be updated as more information is confirmed.