A woman who was five months' pregnant was killed in a head-on car crash by an American serviceman suffering from a sleeping disorder.

Emma James died in the crash on the A420, near Buckland, three years ago tomorrow. Now a coroner has ruled she was unlawfully killed.

An inquest heard US Air Force serviceman David McDuffie had been warned by a doctor not to drive, because he suffered from sleep apnea - a breathing disorder that can increase the risk of accidents because of tiredness.

McDuffie, based at RAF Fairford, in Gloucestershire, was taking colleague Lee Reynolds to the dentist when his white left-hand-drive Hyundai Sonata careered into the path of Mrs James's Ford Focus.

Mrs James, 33, of Buckland, suffered multiple injuries and died at the scene, near Carswell Golf Club.

Off-duty policewoman Sara Kent went to help and said: "It was evident the woman in the Ford Focus was trapped, due to the severity of damage to the vehicle. I advised the driver of the Hyundai to sit down. He turned his back to me and walked away.

"I found it incredibly frustrating I was unable to assist Mrs James. I felt extremely angry towards the driver of the Hyundai for his evasive reaction and indignant attitude towards me at the scene."

McDuffie, 33, who was diagnosed with the condition four years previously, was advised by a doctor that his sleep apnea had begun to deteriorate and that he should not drive while feeling sleepy, the inquest heard.

A statement made by McDuffie in September 2004 was read out. It said: "I cannot give an explanation as to why the car went into the opposite lane and I do not know if I fell asleep."

In a statement, Mr Reynolds said: "I noticed McDuffie appeared tired. He yawned and stretched to try to wake himself up."

Because McDuffie was taking Mr Reynolds to RAF Croughton, north of Bicester, he was technically deemed to be on duty.

Under the Visiting Forces Act, he was tried under American military authority rather than in an English court and was found guilty at a court martial of negligent homicide and causing injury to Mr Reynolds and Mrs Barber.

He was sentenced to one year in prison but served fewer than five months. McDuffie also had his rank reduced, received a bad conduct charge and had since returned to the US.

Recording a verdict of unlawful killing, Assistant Oxfordshire Coroner Dr Richard Whittington said: "This is an offence of the highest order, the equivalent in the UK legal system would be death by dangerous driving."

Speaking after the hearing, Mrs James's family said they were pleased with the verdict of unlawful killing but angry that the man who killed her spent just a few months in prison.

Her mother Lois Terry said words could not describe the feeling of losing both a daughter and an unborn grand-daughter.

She added: "The inquest verdict is the right one. But from the family's point of view we were astonished and disappointed with the sentence McDuffie received two years ago.

"The maximum sentence he could have got was 11 years and he got the minimum. After serving just five months he was sent back to the United States."

Mrs Terry, who lives in Arat, near Melbourne, Australia, with husband Ray, said: "Notwithstanding the fact that this man killed our precious daughter and unborn grandchild, that man was a danger to everyone on the roads that day.

"He knew he had a sleeping condition and he hid it. He was told by an expert medical consultant that his level of sleep apnea had deteriorated and that he was not to drive when he was sleepy, and it was his responsibility to make sure he didn't.

"If I could tell everyone in America about him and his condition, I would warn everybody."

The 63-year-old added: "Emma was a beautiful person in the prime of her life. She was finally pregnant after 10 years of trying.

"The pain will never get any easier to deal with, because she was so special. She had hundreds of friends. She made everyone laugh, because she was such a terrificperson.

"Every day is a struggle for us."

Mrs James' sister Nikki Terry, and partner Harvey Milburn, both of Northamptonshire, attended the inquest.

After the hearing, Ms Terry said: "She was going to be a mum, she knew she was having a little girl which she was going to name Zoe. It has been really hard on my parents, as they were going to be grandparents for the first time.

"I'm pleased with the coroner's verdict. It has taken nearly three years, but even now I don't feel like we have closure."