"But now he is absolutely ecstatic and so are his family."
A Downing Street spokesman said Prime Minister Gordon Brown was "very supportive" of the decision to pardon Mr Shields.
Joey Graney, Mr Shields' uncle, said the family would like to see the Bulgarian authorities re-open the case and for the "real culprit to be caught".
He said: "This lad has lost four-and-a-half stone. Why should a lad, a young innocent lad, have to have gone through what he's gone through?
"There should be a public inquiry into this case and I think the government should pressurise the Bulgarians to re-open this case.
"They know who the real culprit is - everyone knows who it is and he should be made to stand up and face what he really [did]."
Mr Shields has been held in Thorn Cross young offenders institution in Warrington after serving the initial part of his 15-year sentence in Bulgaria.
I have now concluded, having looked carefully at all the evidence..., that Michael Shields is telling the truth when he says he is innocent
Justice Secretary Jack Straw
Mr Straw said that fresh evidence had come to light during a meeting with the Shields family on 28 August.
He was told that two members of the family had visited the home of another man alleged to be responsible for the crime, shortly after the attack in 2005.
"I was told in the course of the visit that the man made an oral confession in front of several other people," Mr Straw said.
"This episode, I was told, happened on 22 July 2005, a day after the start of Mr Shields' trial in Bulgaria.
"I will not set out in this statement all the evidence that has come to light over the last two weeks but suffice it to say that there is very good reason to believe I was being told the truth."
Mr Straw added: "I have now concluded, having looked carefully at all the evidence now available, that Michael Shields is telling the truth when he says he is innocent of the attempted murder of which he was convicted in Bulgaria.
"That being so I have recommended to Her Majesty the Queen that he should be granted a free pardon and she has graciously assented."
Merseyside Police were asked to investigate further and more evidence had "come to light over the last two weeks", Mr Straw added.
Jack Straw: "Michael Shields is telling the truth, when he says he is innocent..."
The police have since sent their evidence to the Bulgarian authorities and Mr Straw is also intending to speak to his counterpart in Bulgaria.
A Ministry of Justice spokesman said the British Ambassador in Sofia had already talked to the Bulgarian administration about the justice secretary's decision.
In 2005 another man, Graham Sankey, originally admitted involvement in the attack on the barman, but subsequently withdrew his statement and now denies any involvement in the attack.
The pardon follows a campaign by the Shields family, MPs, clergymen, Liverpool players and others who believe he is innocent.
Liverpool councillor Joe Anderson, who embraced Mr Shields as he left Thorn Cross, said: "We've reached the milestone but the fight goes on to clear young Michael's name.
"But today is for celebration that we've got him out and it's a fantastic day."
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