When Joseph Lissa came to Britain and claimed asylum he admitted having commanded fighters in a bloody civil war in his homeland of Sierra Leone.
He was initially allowed to stay, but the Home Office later refused further permission to remain. A judge who considered the case ruled that there were serious reasons to think that he "voluntarily participated in killings and rape".
Yet when Lissa - who now works as a driving instructor in Huddersfield - mounted a new appeal he was able to overturn the Home Office's case, on the grounds that he had married a British citizen and fathered a child here.
Critics said that the case showed how human rights laws, drawn up after the Second World War to avoid a repeat of its horrors, can be used by those accused of war crimes to avoid deportation.
The Sunday Telegraph's End the Human Rights Farce campaign has revealed a series of cases in which foreign criminals have been able to win the right to stay in Britain permanently, frequently because they have had children here.
The civil war in Sierra Leone began in 1991 when the Revolutionary United Front (RUF) attempted a violent overthrow of the west African country's government.
The RUF was notorious for its bloodthirsty tactics, which included inflicting gang rapes and amputations on its enemies and civilians, as well as murder and looting.
Intervention by the British Armed Forces in 2000 ensured the RUF's defeat and the implementation of a United Nations-backed peace accord.
Lissa came to Britain in April 2002 and applied for asylum on the grounds that he would be in danger in his homeland. He was refused asylum but granted exceptional leave to stay until 2006.
When that period expired, he applied for further permission to remain, but Home Office delays meant that his case was still unresolved when he married his British wife, Annisa, in 2009, three months after the birth of their son.
He was finally refused leave to remain in December 2010, and lodged an appeal, telling a court that at the age of 17 he was captured by the RUF and forced to fight. He was later involved in fighting in several areas of Sierra Leone and was promoted to sergeant.
Lissa, now 31, admitted that he took part in the RUF's "Operation No Living Thing", in which, he said: "We hit the village in revenge to kill anyone in any village."
The court ruling said: "The appellant says that he never 'killed anyone intentionally' and never killed any unarmed civilians. He acknowledged looting but never raped or killed 'intentionally'."
However, immigration Judge Darrell Shimmin said there were serious reasons for considering that Lissa "voluntarily participated in killings and rape and, with full knowledge, was making a substantial contribution to the crimes committed by the RUF".
Judge Shimmin examined whether he should stay under Article 8 of the European Convention on Human Rights, which protects the right to family and private life. The judge rejected the appeal, but Lissa took his case to the Upper Tribunal Immigration and Asylum Chamber.
The upper court, led by Lord Bannatyne, found that the Home Office's delay reduced the weight of the argument that Lissa, as a war criminal, should not be granted safe haven in Britain.
The court concluded that it would therefore be disproportionate to remove him, and allowed his appeal.
Confronted at his bungalow in a quiet cul-de-sac, Lissa said: "I was not the only child combatant in the RUF. I know what they did to me and members of my family. What do the Home Office know about what went on in the RUF?"
Sir Andrew Green, of MigrationWatch, said: "This is another deeply frustrating case, where a war criminal has been allowed to stay here due to a combination of Home Office delays and human rights legislation."
A Home Office spokeswoman said: "For too long Article 8 has been used to place the family rights of foreign criminals and immigration offenders above the rights of the British public."