Senior Sinn Féin member Bobby Storey has called those who murdered republicans Jock Davison and Kevin McGuigan “criminals” and called on anyone with information to give it to the police.
The party's Northern Chairman Mr Storey held a news conference in Belfast, at which he said the PSNI had no basis for arresting him in connection with Mr McGuigan's murder last Wednesday.
He added he will be taking legal proceedings against the PSNI chief constable.
Mr Storey appeared alongside Sinn Féin President Gerry Adams, Vice-president Mary Lou McDonald, and Deputy First Minister Martin McGuinness.
Mr Storey and two other republicans, Eddie Copeland and Brian Gillen, were arrested last Wednesday by PSNI officers investigating the murder of Mr McGuigan.
All three men were released unconditionally on Thursday evening.
Mr Storey described those responsible for the murders as criminals and enemies of Sinn Féin's peace strategy.
He said the only way to deal with them was through the criminal justice system and urged anyone with information to give it to the PSNI.
He also said the authorities had no basis for arresting him. He claimed that during his detention no shred of evidence or intelligence to warrant his arrest was presented to him and he intends to sue the PSNI.
He also said the IRA had stood down, was now gone and it was not coming back.
Sinn Féin Northern Chairman Bobby Storey says he will take legal action against PSNI over arrest https://t.co/AQgTBK0bfJ— RTÉ News (@rtenews) September 13, 2015
Mr Storey also denied he had been part of any review carried out by Republicans following the death of Mr Davison.
Mr Adams said Sinn Féin will be re-engaging in negotiations tomorrow with a view to addressing the problems that are threatening the peace process.
Sinn Féin has insisted the IRA has gone away and has accused the two Unionist parties of contriving a crisis for electoral gain.
Mr Storey added: "The behaviour of the Unionist parties, who have cynically used my arrest to pull down the political institutions, has been nothing short of disgraceful.
"They have succeeded only in holding the political process to ransom and providing encouragement to the dissident elements and the criminals who murdered Jock Davison and Kevin McGuigan."