A tribunal has ruled that the killer of head teacher Philip Lawrence, 26-year-old Learco Chindamo, should not be deported to Italy where his father was from.
Learco Chindamo could be freed next year
BBC political correspondent Laura Kuenssberg answers the key questions about the case.
On what grounds was the decision not to deport Chindamo taken?
The Home Office had tried to get a ruling that Chindamo would be deported at the end of his sentence.
But his lawyer's attempt to overturn that was successful this week at the Asylum and Immigration Tribunal.
His lawyer persuaded the tribunal, using EU immigration law and the Human Rights Act, that there were not sufficient grounds to force Chindamo to leave the country when his jail term was up.
Why did the Home Office lose the case?
The tribunal disagreed with the Home Office view that Chindamo still presented a risk to the public.
They said he had "not been shown to pose a present and serious threat" even though the Home Office had argued that he did. This issue of his risk was at the heart of the ruling.
How much was human rights legislation/EU immigration legislation involved?
The main argument was that because the tribunal was not convinced by the Home Office evidence that he presented a serious threat to the public, deporting him could not be justified.
That ruling was largely based on a piece of 2004 European law, agreed by ministers and introduced voluntarily by the government into British law last year.
This law reinforces the principles of freedom of movement for EU citizens - but lays down criteria relating to deportations.
Philip Lawrence was killed in 1995
In essence it says that an EU member state cannot deport an EU citizen unless they pose a threat to the "fundamental interests of society" - which usually means terrorism.
In other words, if a convicted criminal can show that he or she is normally resident in the country which is trying to deport him, the courts need to take that into account, along with the risk he or she poses, before sanctioning his/her removal.
The European Convention on Human Rights, the backbone of the British Human Rights Act, also played a part in the ruling.
Article 8 of the convention would have stopped the deportation too, because it says that every citizen has the right of respect for private and family life.
Chindamo was born in Italy, but his family have been in this country for many years.
The tribunal made clear that, in their view, sending him to Italy just because that was the country of his birth would have infringed his rights for a life with his family.
It was not the Human Rights Act which sealed the fate of the Home Office's attempt to deport him - but it could have been invoked were it not for the other law.
What are the government's critics saying, and what is the political impact likely to be?
Home Office ministers are frustrated by the tribunal's decision - but it was their department which brought in the critical EU law on deportations in the first place.
On Chindamo, they say they have been trying to guarantee this deportation since 1999, but have failed.
And although they are appealing the decision, there is no certainty that they'll win it.
Frances Lawrence said she felt "utterly devastated" by the decision
Justice Secretary Jack Straw insists that there is nothing wrong with the Human Rights Act, but there is a flaw in how the tribunal interpreted the law.
It is not the first time that there have been legal decisions that have baffled some of the public when the finger has been pointed at the Human Rights Act.
And it has given the Conservatives a chance to repeat their determination to get rid of it altogether and replace it with a British Bill of Rights.
They say that would act as a guide for the judiciary as to how to interpret the European Convention on Human Rights.
The Conservatives are not suggesting we pull out of that. But many lawyers are sceptical as to how much difference it would make. The European Convention would still supersede any bill of rights.
What happens next?
The government says it will appeal against the tribunal's decision. But that could take months and ministers are just not sure what their chances are of success.
The justice secretary has offered to meet Mr Lawrence's widow next week.