A Scottish-born army veteran accused of killing his parents will try to save himself from execution in America by arguing that he is severely traumatised after fighting in Iraq for the United States.

Derek Connell, from Glasgow, has pleaded not guilty to two counts of first-degree murder after being charged with murdering his mother and stepfather in the US.

Police in Bakersfield, California, found the bodies of Kim and Christopher Higginbotham shot dead in their home on April 30 and arrested Connell as he was seen leaving the property.

Connell, is also alleged to have taken a video of their dead bodies on his mobile phone and sent it to a relative, reportedly his aunt who still lives in Scotland.

Police say Connell confessed to the killings but has pleaded not guilty to two counts of first degree murder as he is suffering from post-traumatic stress disorder (PTSD), after being stationed in the Gulf for more than two years with a US army platoon.

Last night, officials from the Kern County district attorney's office in California, which is prosecuting the case, told the Sunday Herald that the allegation of "multiple murders" made Connell eligible for the death penalty.

Deputy district attorney Arthur Norris stated that he "did not rule" out the possibility of capital punishment being an option if Connell is found guilty.

However, Connell's defence team will mount a defence around PTSD. They say Connell suffers PTSD brought on by traumatic and harrowing combat experiences during his military service in the Gulf.

It will be claimed that Connell suffers from blackouts and self medicates with large amounts of alcohol, after which he does know know what has happened and often begins to panic.

His lawyer Paul Cadman, is expected to draw heavily on Connell's time as a combat soldier and his service in a frontline US army platoon in Baghdad and Fallujah between 2007 and 2009, a period that saw some of the fiercest fighting in the conflict.

Cadman is understood to be preparing his case around a claim that Connell was traumatised by the experience that included the period known as "the surge" when the then US President George W Bush ordered the deployment of more than 20,000 soldiers into Iraq.

The case aimed at saving Connell from being executed will highlight incidences of him seeing fellow troops killed during bloody battles in Baghdad and Fallujah, as well as himself killing Iraqi insurgents in combat situations.

Cadman, a high profile criminal lawyer in California, will use a defence similar to one he employed during a notorious high school shooting at Taft Union High School in Kern County, that saw 16-year-old Bryan Oliver, who walked into a classroom and shot at two students in January 2013, avoid a life sentence without parole.

Public defence attorney Cadman used a diminished responsibility defence to argue that Oliver was pushed to violence because he was tormented by bullies at school, which saw the teenager instead jailed with the possibility of parole after 13 years rather than the whole life-term sought by prosecutors.

Cadman is understood to be planning to mount a "traumatic disorder defence" for Connell, with the principle aim of staving off the death penalty, which remains a legal option in California.

Cadman will argue that Connell, who won campaign medals for service in Iraq as well as taking part in a tour of duty of Afghanistan, has struggled to adjust to civilian life and has been scarred by wartime experiences, particularly deaths he witnessed in frontline combat.

During an initial hearing, Cadman said the failure of authorities to provide his client with proper medical treatment was the 'root' of the double murder case.

"Derek Connell is a highly decorated Iraq war veteran whose experiences in Iraq caused him all kinds of medical and mental conditions," he said.

The U.S. Department of Veterans Affairs failed to get Connell the help he needed upon his return, the attorney claimed.

Connell was born in Rutherglen Maternity Hospital and lived with his mother in Shawlands on Glasgow's south side as a child, although no details of his father were listed on his birth certificate.

His mother worked as a secretary in Glasgow and met her future husband while he was stationed with the US Navy in Scotland.

She moved with her son to be Higginbotham when he went back to America more than 20 years ago and the family settled in California.

Connell, who worked in the oil industry after leaving the US army, has spent most of his life in America, where he attended high school.

He will face a preliminary court hearing on July 26. However, his trial is unlikely to start until for at least a year.

Sources close to Connell's legal team have said that he is "in shock" and is on suicide watch at the Kern County Central Receiving Facility, where inmates are often held during their initial appearances. He is likely to be moved to Lerdo County Jail within the next few months.

Deputy district attorney Norris said that the murder charges were aggravated by the alleged use of a firearm, as he set out what is likely to be a protracted legal process facing Connell.

Naomi McAuliffe, Amnesty International's Scotland programme director issued called on prosecutors to rule out the use of the death penalty in light of Connell's post-traumatic stress disorder.

She said:"If Derek Connell is found to be suffering from mental illness, it is worth noting that executing people with mental illness is clearly prohibited by international law but the US has executed dozens of prisoners known to be suffering from severe mental illness."

Meanwhile,a Foreign and Commonwealth Office spokesman added: “We are in contact with local authorities following the detention of a British man in connection with a murder case in Bakersfield, California."