Sinn Fein is standing by its position that John Downey should never have been arrested as political outrage grew across the UK that almost 200 on-the-run republicans have been granted so-called 'get out of jail free' cards.
The party has poured scorn on unionist claims they knew nothing about the controversial 'comfort letters'.
He said that unionists – including the First Minister Peter Robinson – must have known about the deal.
He said: "It was very public and for the unionists to claim they knew nothing about it is false.
"(Mr Robinson) knew about the OTR situation, he knew they were crucial to the peace process and the political process. He is foolish and needs to be careful as a political leader painting himself into a corner on the issue."
He said people have to come forward and ask if they are still being sought by the authorities.
Mr Maskey said the issue had been raised at talks after talks, adding that leading unionists were aware of the letters. He pointed out it had been mentioned in the 2009 Eames-Bradley Report on dealing with the past.
Referring to Peter Robinson's threat to quit over the issue, he commented: "Peter can resign if he wishes, but that is still not going to address the past."
"A process was put in place to deal with outstanding cases, including that of John Downey," he said.
"The arrest of John Downey by the London police was in clear breach of this and of the commitments given by the British Government in 2004, during the peace process negotiations at Weston Park and in subsequent negotiations.
"John Downey should never have been arrested and this has been vindicated by the court decision."
Earlier yesterday, Deputy First Minister Martin McGuinness indicated that he felt unionists were overreacting when he issued a message on Twitter urging them to "calm down".
The leading Sinn Fein politician posted: "My unionist colleagues need to calm down.
"We've all come a long way.
"No sensible person will thank anyone for threatening the institutions."