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SAN DIEGO — Two Marines, a captain and a master sergeant, have been relieved of command in connection with an explosion at Camp Pendleton that killed four enlisted personnel during a training exercise, a report on the incident said Thursday.

The Nov. 13 explosion was probably caused when a grenade round was “dropped, kicked or bumped,” the report said.

The four Marines killed were explosive ordnance disposal specialists assigned to clear rounds from a training area on the base.

All four Marines had deployed to combat zones and been awarded a Combat Action Ribbon, awarded only to Marines who were under fire and returned fire.

Those killed were:

Staff Sgt. Mathew Marsh, 28, of Long Beach. He deployed twice to Iraq and twice to Afghanistan.

Gunnery Sgt. Gregory Mullins, 31, of Bayou L’Ourse, La. He deployed twice to Afghanistan.

Sgt. Miguel Ortiz, 27, of Vista, Calif. He deployed to Iraq and Afghanistan.

Staff Sgt. Eric Summers, 32, of Poplar Bluff, Mo. He deployed to Iraq and three times to Afghanistan.

The four had a total of seven children, all under age 10. The Marine Corps Scholarship Foundation has awarded each child $30,000 in college scholarship support.

Two other Marines and a Navy corpsman were injured in the accident and were treated and released after receiving medical assistance at the scene.

The Marines had been assigned to clear away unexploded ordnance on the Zulu range on the sprawling base. Clearing away ordnance is a basic maintenance chore in preparation for using the range for training.

According to the report, the captain and master sergeant had failed to adequately assess the potential danger. The decision to relieve them of command could end their careers.

Read more at latimes.com.