Robert Bales the US soldier accused of killing 16 Afghan civilians

Staff Sergeant Robert Bales, left, is the soldier alleged to have killed 16 Afghan civilians as they slept

This photo appears to show Bales, left, participating in a training exercise before his deployment to Afghanistan in December

Arrival: A van believed to be transporting Bales leaves Kansas City International Airport on Friday evening

Robert Bales is a highly decorated staff sergeant in the American army, but now he could face the death penalty if convicted of murders

The home of Robert Bales, the US soldier accused of killing 16 Afghan civilians, in Lake Tapps, Washington, stood empty last night.

The family of the 38-year-old sergeant, who has plunged US policy in Afghanistan into one of its worst crises, has been moved to Lewis-McChord army base where Bales's unit, the 3rd Stryker Brigade, has its headquarters. Now his house is up for sale.

The first journalists from a Fox news affiliate – the network that revealed his name after a six-day blackout imposed by the Pentagon – found neighbours surprised and baffled by the revelation that the man they knew as Bob was accused of massacring women and children during a murderous rampage through a village in Afghanistan's Panjwai district.

"Bob's a normal guy," former neighbour Paul Wohlberg told Fox. "Not normal now but, yeah ..." Another neighbour, Kassie Holland, told US media: "He always had a great attitude about being in the service. He seemed just like, yeah, it's my job, it's ... what I do."

The picture of Bales that is emerging is a long way from the man who spoke to the Northwest Guardian three years ago after the battle of Zarqa in Iraq, when he insisted that what differentiated soldiers like him from those they were fighting was the ability to distinguish between combatants and civilians. "I've never been more proud to be a part of this unit than that day," Bales said in that article. "We discriminated between the bad guys and the non-combatants, and then afterwards we ended up helping the people who three or four hours before were trying to kill us.

"I think that's the real difference between being an American as opposed to being a bad guy, someone who puts his family in harm's way like that." If there was any hint that Bales was suffering problems, it was not picked up. He had been charged with assault in 2002 and asked to attend an anger management course, while in 2008 he is reported to have fled the scene of a car crash.

And in the end, and by his own criteria, it appears that Bales became one of the bad guys, reportedly leaving Camp Belambay near Kandahar at 3am last weekend, wearing night-vision goggles, to enter three houses in two villages whose occupants he allegedly slaughtered. The question that will be asked now is what happened, not least because Bales is reported to have undergone mental health screening five years ago before being assigned to sniper training.

The revelation of Bales's name, details about his career and family life emerged as he was flown back to the US to a military prison in Fort Leavenworth, Kansas, His lawyer confirmed that Bales might face the death penalty if convicted of the murders.

Bales is a highly decorated soldier and trained sniper who had served four tours in Iraq and Afghanistan. The killing spree he is alleged to have undertaken has plunged relations between the US and Hamid Karzai, the Afghan president, to a new low.

What precisely happened to the "good, fun guy" – as Bales's neighbours described him – will be the focus of his defence amid suggestions both from officials and his own lawyer, John Henry Browne, that they would suggest that post traumatic stress disorder may have been a contributory factor.

Bales, who volunteered for the army two months after the 9/11 attacks, lost part of a foot and reportedly suffered a traumatic brain injury during his three tours in Iraq and had seen a colleague lose a leg in Afghanistan just before the rampage in Panjwai.

Bales was first deployed in Iraq in November 2003 when his unit spent a year in Mosul. In June 2006 he was deployed in Baghdad and then in Baquba, one of the most dangerous places in the country. His final Iraq deployment was from September 2009 to September 2010 in Diyala province.

Browne has also said that he had been reluctant to go on a fourth combat tour before being deployed to the operations in Afghanistan. "I am confused why they would send him to Afghanistan," Browne said. "There was no 'maybe he shouldn't go' discussion."

Indeed after his return from Iraq his wife, Karilyn, had written a blog in which she said that she hoped he would be able to have some choice of where the family moved next. They were getting ready to move in the summer of 2011 and hoped that the army would allow them some say over where they went. Germany, Italy, Hawaii – Kentucky to "be near Bob's family" – or Georgia "to be a sniper teacher". Instead he was deployed to Afghanistan.

The killings in Afghanistan have come amid escalating concern over an epidemic of suicides and PTSD among US military veterans of the decade-long wars in Iraq and Afghanistan.

Last Wednesday another Iraq veteran, Abel Gutierrez, killed himself after murdering his 11-year old sister and his mother after police said "he just snapped" having suffered nightmares and periods of aggression since his return to the US.

Of particular concern is the increased risk of PTSD in soldiers who are deployed on multiple occasions. PTSD is known to be "dose dependent" – the risk of suffering from it increases after more exposure to its triggers.

Indeed, according to a recent study by the US Armed Forces Health Surveillance Centre in Silver Spring, Maryland, PTSD during a third deployment is double the rate, among male members of the armed forces, than that found after a single combat deployment. While its incidence appears to decline in fourth deployments, that is only because of the significant dropout after three tours of those already diagnosed with problems.