Senior officers have escaped prosecution over the deaths of 14 British servicemen in a Nimrod aircraft crash – the single biggest loss of life since the Falklands War. RAF investigators have told grieving relatives they were frustrated in their attempts to hold one high-ranking officer to account, due to his seniority and refusal to answer questions when interviewed.

Despite reports that a senior officer could face a court martial last year, the individual concerned, Air Commodore George Baber, never faced disciplinary action. He was criticised in an official inquiry into the crash of the Nimrod, which exploded after air-to-air refuelling over Afghanistan in 2006. The inquiry concluded that the mid-air blast was caused by leaking fuel coming into contact with a hot air pipe.

The report, by Charles Haddon-Cave QC, criticised the Ministry of Defence for sacrificing safety to cut costs. Air Commodore Baber was one of those singled out for criticism in the report, which said he bore the "lion's share of the blame" for failing to give "adequate priority, care and personal attention to the preparation of the NSC [Nimrod Safety Case]. He failed to give the NSC the priority it deserved. In doing so, he failed, in truth, to make safety his first priority."

The inquiry cited "incompetence, complacency and cynicism" as being at the root of the deaths.

According to a new book by Trish Knight, whose son Ben was 25 when he died in the crash, a letter from the RAF Police said that they thought there may be sufficient evidence to support a charge against a former head of the Nimrod Integrated Project Team. In the book, The Crash of Nimrod XV230: A Victim's Perspective, Mrs Knight accuses the Government of giving "the illusion of justice" but delivering none, condemns the MoD for putting "cost before lives", and says: "For us, justice will only have been done when those people responsible for the death of Ben have been held to account."

She details how RAF investigators gave her and her husband, Graham, hope last year, only for it to be later dashed. She says a senior RAF investigator told them the investigation was "complicated" because of the seniority of Air Commodore Baber, who had "replied 'no comment' " to every question he was asked. The officer also said that nearly all of those approached for statements refused to co-operate. In the case of staff from BAE, the aircraft manufacturers, Mrs Knight claims she was told that each had provided "identical letters, stating that they didn't wish to help in the investigation". She adds that the RAF investigator gave the "impression that, had everyone involved been prepared to provide a full and frank testimony, the outcome may have been very different".

The Knights had been told there was not "a realistic prospect" of convicting the Air Commodore, who has since retired from the RAF and now has an executive role with a leading MoD equipment supplier.

Those who did not co-operate "will have to live with their consciences for the rest of their lives," Mrs Knight said.

A BAE Systems spokeswoman said "there was no legal obligation" for employees to take part in the RAF investigation.

The MoD said: "Our thoughts remain with the families of the crew of Nimrod XV230. As a result of the Haddon-Cave review, the MoD has made substantial improvements to airworthiness procedures, including the establishment of an independent safety regulatory body – the Military Aviation Authority."

Speaking yesterday, Mrs Knight said the death of her son left her feeling "as if I had been thrown into a bottomless pit and I just kept falling deeper and deeper into the darkness that was hell". She added: "People talk about 'closure', but I know from bitter experience there is no such thing."