Hyrone Hart, 28, and Kurt Roberts, 19, were found guilty of shooting dead a woman in front of her two children at her London home. The killers were described as "an affront to civilised society" and part of an "execution squad" by a judge at the Old Bailey.
Police revealed after the case that the men, who had used false names when they arrived in the country last year, where part of a nine-strong "mix and match" Jamaican Yardie gang that had come to Britain to carry out violent robberies against suspected drug dealers and rich black people.
Eight of the gang have now been jailed and the ninth has been deported to Jamaica.
Scotland Yard issued a warning over the increase in armed Jamaican criminals secretly entering the United Kingdom, who have been linked to up to 28 drug-related murders in London this year. Tougher measures to prevent Jamaican gangsters entering the UK were put in place recently.
Hart and Roberts were convicted of shooting dead Avril Johnson, 30, at her home in south London in July last year. The couple were also found guilty of the attempted murder of Mrs Johnson's husband, Kirk, who escaped by playing dead when a bullet meant for him missed by inches and hit a wall. The couple's daughters, aged seven and one, were pushed under a mattress next to their parents during the shooting.
The Common Sergeant of London, Judge Neil Dennison, ordered Hart to be jailed for life and Roberts to be detained in youth custody for life for the murder. Judge Dennison told them: "Your conduct was an affront to civilised society. You were part, in effect, of an execution squad."
Hart was also found guilty of murdering a trainee plasterer, Patrick Ferguson, 34, and given a second life sentence. Roberts was found guilty of raping a robbery victim in Clapham, south London, and detained for 10 years. Both offences occurred during a five-week crime spree.
But the jury could not agree on murder charges involving Michelle Carby, 35, who was found tied up and shot through the head at her home in Stratford, east London, four days after Mrs Johnson's murder. The men may have to face a retrial on that charge.
The killers used a Chinese Tokarev 9mm self-loading pistol that had supposedly been deactivated and made safe.
One of the key pieces of evidence against the men was a series of calls Hart made to his girlfriend in Jamaica on two mobile telephones stolen from the murder scenes.
Initially the police did not know the identity of the two suspects and a national hunt was set up to track them down. Hart was eventually arrested after undercover officers identified him at an address in Handsworth, Birmingham.
Both men came to Britain from Kingston, Jamaica.
Hart arrived on 28 March last year using a stolen passport with the false name of Anthony O'Neil Rowbotham.
Immigration officials suspected he was an illegal entrant and gave him 24 hours to return to Jamaica but he went to live in London.
He was found to have convictions in Jamaica for robbery with violence, burglary and escaping custody.
Roberts entered the country under the name of Joseph Anthony Lee on 6 May 1998 alongsidse three other Jamaicans, two of whom have since been convicted of robberies from drug dealers.
Roberts was given six months' leave to remain in Britain to see his mother.
Scotland Yard detectives discovered that Jamaican gangsters have been using counterfeit and stolen passports to enter Britain.Reuse content