Christopher Jefferies said:
It provides an important conclusion to the whole aftermath of what I had to go through following my arrest.
As the letter itself explains it provides the public vindication which was not given at the time I was released from police bail.
Although the letter is addressed to me and is therefore expressing regret at what I had to endure, the letter also implicitly provides the public acceptance that the events didn't just affect me but affected a large circle of my relatives and friends.
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Five people were killed and dozens more were injured after a car and knife attack in the capital on Wednesday afternoon.
Among those expected to attend the ceremony will be former US President Bill Clinton and ex-Northern Ireland first minister Peter Robinson.
Five people have been killed and 40 injured after a car and knife attack in London on Wednesday.