Executed this year in Georgia, Andrew Brannan is one of hundreds of US soldiers who serve, come home from battle with mental scars, commit murder and are put to death.

Some 300 military veterans are currently awaiting execution in the United States, making up an estimated 10 percent of death row inmates, according to a report out Tuesday.

Courts rarely take into account the psychiatric state of battle-scarred veterans, according to the Death Penalty Information Center (DPIC).

A video of Brannan's behavior when he was stopped for speeding on January 12, 1998 gives some insight into his state of mind.

In the footage, taken by the dashboard camera of police officer Kyle Dinkheller, Brannan emerges from his pickup truck and starts dancing crazily, trying to provoke the officer and refusing to follow orders.

Leaving a vehicle when stopped by a police officer is forbidden in most US jurisdictions.

"Fuck you!", Brannan shouts, "I am a fucking Vietnam Veteran!"

Once back in his car, Brannan grabs a weapon. Gunfire breaks out.

Dinkheller is hit nine times and dies on the spot. Brannan, with a wound in the abdomen, gets back in his pickup.

The video is shown at police training academies.

At the trial, Brannan's lawyers tried unsuccessfully to secure lenient treatment based on extenuating circumstances. Decorated for his bravery, Brannan had been diagnosed with post-traumatic stress disorder (PTSD).

- From glory to infamy -

"Given that less than seven percent of the US population are veterans, very often judges, juries, prosecutors and even defense attorneys are essentially unfamiliar with the military experience," Art Cody, Legal Director Veterans Defense Program at the New York State Defenders Association, told AFP.

"There may be a perfunctory acknowledgment of veteran status, but very often judicial decision makers lack sufficient understanding of how the military background and experience has affected the veteran-defendant and the crime with which he or she is charged," he said.

Of the 1,400 people executed since the United States reinstated the death penalty in 1976 -- many were decorated soldiers before their downward spiral.

Such was the case of Robert Fisher, a Vietnam War veteran. President Lyndon Johnson awarded Fisher a Purple Heart for combat wounds he received in 1967. Thirteen years later, suffering from mental illness, Fisher killed his partner.

According to the DPIC report, more than 800,000 Vietnam veterans have signs of PTSD. Another 300,000 Afghanistan and Iraq war veterans are also suffering from the disorder. Traumatic brain injuries are also common among the second group.

"A significant percentage of combat veterans have brought their wars home with them in the form of combat trauma," said Brockton Hunter, a former army scout, attorney and co-founder of the Veterans Defense Project.

"Untreated, and often self-medicated with alcohol or drugs, these veterans can fall into self-destructive, reckless and, sometimes, violent behavior against their communities," he said.

- From one sniper to the next -

In one of the most notorious such cases, John Allen Muhammad, a Gulf War veteran was sentenced to death for 10 sniper killings, mostly in the Washington DC area, that stunned the country.

Muhammad had outfitted the trunk of an old Chevrolet to be able to lie down inside and shoot at people apparently picked by chance. Nicknamed the "Beltway Sniper" for the October 2002 shootings, Muhammad was executed in 2009.

Several experts consulted by AFP said it was unclear how direct a link could be drawn between traumatic experiences on the battlefield and violent acts committed by soldiers years later.

Indeed "the data on violence among veterans with PTSD suggests that alcohol, drug misuse, or other psychological problems are more likely contributors to violence," said Lauren Jenkins, a veterans advocate with ScoutComms, a public relations firm that supports veterans.

The difficulties many veterans face as they rejoin civilian life was addressed in Clint Eastwood's hit movie "American Sniper" with his focus on Chris Kyle, the most lethal sniper in US history.

Kyle himself was killed by Eddie Ray Routh, a former Marine with mental problems. Routh was sentenced in February to life in prison.

His case, according to the DPIC, shows that there can be a different approach, as the prosecutor did not seek to have Routh put to death.