The government will challenge "robustly" the decision to allow the man who knifed head teacher Philip Lawrence to death to stay in the UK.
Learco Chindamo came to the UK when he was six
Home Office Minister Tony McNulty said Learco Chindamo had forfeited his rights because of the seriousness of the crime he committed.
The 26-year-old is serving a life sentence for the 1995 killing.
His lawyers argued that deporting him to Italy, where he was born, would breach his human rights.
Chindamo, who was jailed for life in 1996 with a minimum 12-year term, could be released early next year if the Parole Board decides it is safe to do so.
Mr McNulty said he did not think flaws with the Human Rights Act had resulted in the decision of the Asylum and Immigration Tribunal.
He said: "I don't think it's actually the act that's at fault here.
"It's like a whole range of these things it's the interpretation of the act.
"And we're very clear that with rights come responsibilities and I would think that given the serious and heinous nature of this crime, the individual has forfeited any right to domicile in the UK.
"And I think most people would agree with that, and that's why we'll be asking the tribunal to look again."
Mr Lawrence's widow said she was "unutterably depressed" by the ruling
Philip Lawrence was killed in 1995 as he helped a pupil
However, the human rights lawyer David Enright said under the current rules, it was impossible for people to be deported from one EU country to another.
He also dismissed the government's protests as "posturing", saying it had accepted the 2006 European Commission regulation into British law.
"(This) said that any EU national who had lived in the UK, even in prison, for more than 10 years, could only be removed from Britain on imperative grounds of national security - which clearly would not include Mr Chindamo or anyone like him," he added.
Chindamo was told the news at the weekend and was said to be "pleased" because his "family and life were in the UK".
In a statement he said he hoped the decision would not "cause grief" to Philip Lawrence's widow Frances or to the rest of his family and went on to express his deepest sympathy.
But Frances Lawrence has said she was "devastated " and "demoralised" by the ruling, saying the Human Right Act had "failed to encompass the rights of my family".
Chindamo came to the UK when he was six. His father is Italian, his mother is from the Philippines and he has an Italian passport.
He was 15-years-old when he stabbed Mr Lawrence as the teacher defended a pupil outside St George's Roman Catholic comprehensive school.
Chindamo's lawyers said the Home Office wanted him returned to Italy when he was freed from prison.
But they successfully argued the move would have been illegal as Chindamo was from a European Union country and had already lived in the UK for 10 years by 1995.
Chindamo's lawyer Nigel Leskin said his client was now a reformed character who was unlikely to offend again.
"He was involved in a gang when he was young. He was a kid trying to act up big. He was out of control and he thought he knew everything. He now realises how wrong he was."
It was the second time the government had tried to remove Chindamo - an attempt in 2001 was blocked because it began too soon after he had been sentenced.
A year after her husband's death Mrs Lawrence set up the Philip Lawrence Awards to honour young people's efforts in tackling social issues.
She added: "I am deeply concerned for everything I have worked for, including the setting up of the Philip Lawrence Awards.
"I feel as if I can't fight any more - I feel I can't survive this."
Shadow Home Secretary David Davis added: "It is a stark demonstration of the clumsy incompetence of this government's human rights legislation that we are unable to send a proven killer back to his own country, especially when that country is in the EU."