The widow of a man who shot a fellow soldier up to 10 times before turning the rifle on himself has blamed his actions on anti-malaria medication.
Sergeant Busuttil was shot as he lay in a hammock
Corporal John Gregory, aged 30 years, went berserk following a row with Sergeant Robert Busuttil just days before he was due to leave Afghanistan where he was posted on peace-keeping duties.
Busuttil, 30, of Tycoch, Swansea, died after being shot with an SA80 rifle.
The inquest at Chippenham in Wiltshire heard that Gregory, from the Royal Logistics Corps, had been drinking.
Gregory left the small tented area at Kabul International Airport after the argument and returned soon afterwards with his loaded gun.
The inquest at Chippenham in Wiltshire, heard how Gregory, from Catterick, was two-and-a-half times over the drink drive limit - despite orders rationing beer to just two small cans a day.
But, giving evidence on Tuesday, his widow Annette, 31, said the anti-malaria drugs he had been taking had affected his moods.
She refuted claims from other soldiers that her husband had been aggressive and could get "punchy" when drunk.
"My husband was not really a heavy drinker. He would drink wine at home or beer in social occasions," she said.
Recalling the horrific events of 16 August, Mrs Gregory said: "What happened just wasn't John. He would never do anything so completely rash and irresponsible.
"We had been in constant contact and he was looking forward to coming home very much."
She blamed the horror shooting on his anti-malaria tablets, Chloroquine and Trognanil, which he had been given by the British Army before going to Afghanistan.
"I think the anti-malaria tablets could have been a factor here - there is no other way to explain it."
She told of the litany of side-effects which her husband of seven years had suffered since taking the tablets.
She said: "John became quite paranoid. Every time the phone rang he wanted to know who it was and he would change his e-mail passwords all the time.
"He became mistrusting of everyone and he had great trouble sleeping.
"He had gone to see the medical officer about this and had been told, although the side effects were bad, malaria would have been worse, so he carried on."
Referring to the drugs, pharmacologist Colonel Graham Stewart, of the Royal Army Medical Corps., said: "Chloroquine can rarely cause psychotic effects in individuals but this is not fully understood.
"I estimate it to be a 1/500,000 chance," he said. "It is much more likely that Corporal Gregory's psychotic episode was the result of the direct ingestion of alcohol."
However, the inquest heard that Cpl. Gregory could bear a grudge over a prolonged period of time.
Giving evidence, Sergeant Dale Garner told the inquest he had been warned, before joining the unit, that Gregory could become "punchy" when drunk.
"There was one example of aggression with John. He came to see me one day and said 'I should smack your lights in'.
"I found out that he was referring to a comment I had made a month before. He calmed down and later apologised."
The inquest heard how soldiers in Kabul - and especially the 12 stationed with the Bulk Fuel Installation at Bagram Airport - often flouted the so called "two can" drinks rule.
Many NCO's testified that the rule was relaxed as long as soldiers were fit for duty the following day.
However, claims that this was done officially were denied by Warrant Officer Ricki Ecott, the RSM in overall command of discipline in Afghanistan.
Giving evidence he said: "People are giving the impression that it was some kind of mini Falaraki. It wasn't.
"There were only two incidents where soldiers were seen talking rather loudly in the bar area. It was my job to see that soldiers knew the rules but ultimately if a soldier wanted to get extra drink he could from the German or French bars."
A weapons expert, however, was critical about unit policies which allowed soldiers to have easy access to their loaded rifles whilst being able to drink.
Captain Andrew Riddell, of The Small Arms School Corps, based near Brecon, south Wales, said: "This was a very unusual situation. Mixing alcohol with loaded weapons is a lethal cocktail."
The inquest was adjourned until Wednesday.