Marines charged with murder over Afghanistan death British soldiers in Helmand: the incident took place last year but it is thought investigators only began inquiries in recent weeks. Photograph: Corporal Barry Lloyd Rlc/AFP Five Royal Marines have been charged with murder over the death of an insurgent in Afghanistan in 2011. Seven marines were arrested on 11 October by the Royal Military police. Two more were later arrested, one on Friday and one on Saturday. Four have been released without charge pending further inquiries, the Ministry of Defence said. The incident took place in Helmand province last year, but it is thought investigators only began an inquiry in recent weeks. An MoD spokesman said: "The Royal Military police has referred the cases of the remaining five Royal Marines to the independent Service Prosecuting Authority. Following direction from the SPA these marines have now been charged with murder and they remain in custody pending court proceedings. "It would be inappropriate to comment further on this ongoing investigation," the spokesman added. The soldiers, believed to be members of 3 Commando Brigade, were arrested in connection with an incident described as "an engagement with an insurgent," with no civilians involved. During a six-month tour of duty in 2010, which lasted from April to October, seven servicemen from 3 Commando Brigade were killed in action, all from 42 Commando. The tour, Operation Herrick 14, was the unit's fourth and saw the force score notable successes in capturing explosives from the Taliban. The rules of engagement, largely derived from the Geneva conventions, dictate under what circumstances British troops are allowed to open fire, whether to prevent an attack by the enemy or in direct contact. The arrests are thought to be the first time UK servicemen have been held on suspicion of such charges during the conflict in Afghanistan. A Territorial Army soldier was investigated by military officials after shooting dead a suspected Taliban bomber in the Nahr-e-Saraj area of central Helmand in the summer of 2010. Senior officers believed the man may have been an innocent farmer. But after an 18-month inquiry no charges were brought against Fusilier Duane Knott, who said he had no regrets over his action.