British Prime Minister says the collapse of case against John Downey was down to a “dreadful mistake”

The British Prime Minister says the collapse of a case against the Hyde Park bombing suspect was down to a “dreadful mistake”.
John Downey, who’s from county Donegal, avoided prosecution because of a letter he was sent by police, saying he was not wanted for arrest.
4 soldiers died in the IRA attack in London in 1982.
David Cameron says the letter should never have been sent:

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