L/Cpl Mathew Ford was brought up in North East Lincolnshire
The family of a Royal Marine killed in service in Afghanistan is taking legal action against the Ministry of Defence.
L/Cpl Mathew Ford, 30, from Immingham, North East Lincolnshire, was shot during an attack on a Taliban fort in Helmand province in 2007.
It was believed the marine was accidentally shot by a member of his own team but a coroner gave a narrative verdict at an inquest last year.
His mother Joan said the MoD had failed to answer how and why her son had died.
Mrs Ford, who is taking civil action against the MoD for negligence, said her solicitor had filed papers and the MoD had until 5 November to respond.
She said: "You can't grieve because basically you don't know what happened to him."
L/Cpl Ford, of 45 Commando, had been taking part in a raid on a Taliban stronghold when he was shot in January 2007.
His body was recovered in a rescue mission after three colleagues and a Royal Engineers officer strapped themselves to the sides of two Apache helicopter gunships to get him back when he was left behind.
At the time the MoD said his death was likely to have been a so-called friendly fire incident.
A Royal Navy Board of Inquiry report last August was highly critical, highlighting confusion during the operation, poor preparation and inadequate training.
The report said it was almost certain that L/Cpl Ford was killed by a shot from a British gunner who was on top of an armoured vehicle, but the actions were attributed to a "momentary error of judgement".
The marine's mother Joan Ford says the MoD has failed to answer how and why her son died
In the inquiry into why the gunner had opened fire on his own men, the MoD examined whether a shortage of night vision goggles had contributed to this.
It concluded the gunner had been issued with night vision goggles but had been ordered to put them away because it was getting lighter.
But a Marine told the inquest that "there was poor visibility and the need to use night vision goggles".
Mrs Ford said: "I think it was one cock-up after another that day and basically they [MoD] don't want it to come across that they didn't know what they were doing.
"They know what happened on that day and they should come clean and they should tell us."
In a statement, the Armed Forces Minister Bill Rammell said: "This incident has been the subject of extensive investigation, including a Board of Inquiry to learn lessons, and an inquest to determine the cause of death which had the MoD's full co-operation.
"I remain committed to meeting the family of L/Cpl Ford to discuss their concerns, and we are currently working to find a suitable date.
"As legal proceedings have begun it would be inappropriate for me to comment further at this stage."
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.