A whistleblower told the security firm G4S not to employ a security guard who went on to kill two of his colleagues in Iraq, it has been claimed. Families of the men have asked for G4S to be prosecuted for corporate manslaughter.

According to a BBC investigation, the whistleblower repeatedly warned G4S (operating under the name ArmorGroup) about the guard’s unstable behaviour and convictions as a “violent criminal”. One e-mail said: “I am alarmed that he will shortly be allowed to handle a weapon and be exposed to members of the public. I am speaking out because I feel that people should not be put at risk.”

Another e-mail said: “You have not taken my advice and still choose to employ him in a position of trust. I have told you that he remains a threat and you have done nothing.”

One of the victims’ parents said of the guard: “He fired the bullets but the gun was put in his hand by G4S ArmorGroup. They put the gun in that man’s hand. I want G4S to be charged with corporate manslaughter and be held accountable for what they did. The people who we feel are responsible, who we hold responsible for putting that gun in [his] hand, are without a shadow of a doubt G4S.”

G4S confirmed that the killer had “falsified and apparently withheld material information during the recruitment process” and his screening was not completed in line with the company’s procedures.

“Our screening processes should have been better implemented in this situation but it is a matter of speculation what, if any, role this may have played in the incident,” the company said.