Everyone - the father, the son, the army - agrees that three tours of Iraq drove ­Sergeant John Russell to the edge.

But what pushed him over, into shooting dead five of his comrades in an army that was his life for 16 years, is a matter of bitter dispute.

The military has suggested that ­Russell's work cannibalising and rebuilding robots used to set off roadside bombs brought him into regular contact with gruesome casualties, and that took a toll that exploded at Camp Liberty in ­Baghdad this week.

The army says it recognised signs of trauma in the 44-year-old sergeant, who was just a few weeks from leaving Iraq, and dispatched him for psychological assessment at a military stress centre in Baghdad. Russell got into a fight there, grabbed a gun and shot two doctors and three other soldiers dead.