( CNN ) -- Human error is to blame for a mortar round explosion that killed seven U.S. Marines and injured eight other service members during a training exercise in Nevada this year , the Marines said on Wednesday . An investigation of the March 18 incident at Hawthorne Army Depot revealed that `` the Marines employing one of the mortars did not follow correct procedures , resulting in the detonation of a high explosive round at the mortar position , '' the Marines said in a statement . `` The investigation also determined that the mortar section had not conducted appropriate preparatory training leading up to '' the nighttime training session , the Marines said . The mortar system itself functioned properly , the investigation determined . The Marines were killed when a 60mm mortar round exploded `` in the immediate vicinity '' of a firing position , the Marines said . Earlier this month , the Marines announced that three Marines were relieved of their duties after the incident . On Wednesday , the Marines said they were relieved because their commanding general `` lost trust and confidence in their ability to ensure proper preparation for , and conduct of , live fire training events . '' No criminal charges are anticipated , the Marines said . Those relieved included Lt. Col. Andrew McNulty , the officer in charge of the killed Marines ' infantry battalion -- 1st Battalion , 9th Marine Regiment . Also relieved were Capt . Kelby S. Breivogel , who commanded Company A , and Chief Warrant Officer-3 Douglas H. Derring , the battalion Marine infantry weapons officer . The Hawthorne Army Depot , about 140 miles southeast of Reno , is used for storing ammunition and weapon stocks awaiting demilitarization . The facility also provides high desert training facilities for military units . CNN 's Jason Hanna contributed to this report .
In March , seven Marines died during training exercises . Marines did not follow correct procedures , investigation said . No criminal charges are anticipated , the Marines said . Earlier this year , two Marines were relieved of duty due to the incident .