A security guard who murdered two ex-servicemen in Iraq was not vetted properly by his employer, a coroner said.
Danny Fitzsimons shot dead Paul McGuigan and Darren Hoare, in 2009, after the private firm employed him.
The ex-paratrooper, of Greater Manchester, employed by ArmorGroup, is serving a 20-year jail term in Baghdad.
The coroner has ruled Mr McGuigan, from Peebles in the Scottish borders, was unlawfully killed.
The Stockport inquest, which began in September last year, heard Fitzsimons, of Rochdale, had a history of criminal offences and there were ongoing proceedings against him at the time he travelled to Iraq.
Coroner Joanne Kearsley described him as a "highly manipulative individual" who had provided inaccurate information to his employers.
However, his documentation was not checked by the G4S-owned firm, nor did human resources staff check to make sure they had all the relevant paperwork, she said.
Ms Kearsley dismissed Fitzsimons' claim he was suffering from post-traumatic stress disorder or acting in self defence when he murdered Mr McGuigan, 37.
The Manchester South coroner also said the 34-year-old was not adequately managed by the Probation Service.
The court has previously heard the men were shot by Fitzsimons after "good natured rivalry" about their former regiments escalated into violence.
A steroid user, described as violent and unpredictable, especially when drunk, Fitzsimons held extreme racist views, and according to one doctor's assessment only showed any excitement when talking about involvement in football hooliganism and firing guns.
In pages of writings recovered by police from his home, he had written: "I have lived a life of violence. Any chance I have to do someone I will take it."
After the inquest verdict, a spokesman for G4S said Mr McGuigan's death had come as "a profound shock" and offered "sincerest sympathies" to his family.
"Industry standards for the recruitment of private security operators in high-threat environments have advanced significantly in the years following this tragic incident. G4S has played a key role in promoting those changes," he said.
"G4S takes the safety of our employees and the people in our care extremely seriously and we operate rigorous recruitment processes. We will continue to advocate for the adoption of the highest possible industry standards in the screening and vetting for armed security roles."
Mr McGuigan's mother Corinne Boyd-Russell travelled from Scotland to hear the coroner's verdict. Members of Fitzsimons' family, from Rochdale, also attended.
Mrs Boyd Russell, 62, said: "G4S is the third largest private sector employer in the world. It's time these rich and powerful organisations were properly accountable and that should start with an apology to all of us, to Paul's family.
"We've never had an apology after five and a half years."
The inquest earlier heard how Fitzsimons had shot the men dead within 24 hours of his arrival in Baghdad.
Another security guard, Kevin Milsom, told the hearing how the men were drinking and exchanged "banter" about their former regiments before Fitzsimons and Mr McGuigan, a former Royal Marine, squared up to each other.
Mr Milsom said he then stepped in to calm things down, before returning to bed and falling asleep drunk.
Shots were then heard in the night, and Mr Milsom was woken in the morning by a colleague, who said: "Your mate has just killed two of our blokes."