Gerry Adams said that the release of Bobby Storey served to highlight the “contrived nature” of the current political crisis.
The Sinn Fein leader was speaking after Mr Storey, the party’s northern chairman, was freed unconditionally by police.
He had been arrested on Wednesday by officers probing the shooting of Kevin McGuigan on Wednesday, August 12, as he arrived back at his home with his wife at Comber Court in the republican-dominated Short Strand.
In the wake of his release, Mr Storey’s lawyer said his client intended to sue for wrongful arrest.
Two other arrested men – well-known republican figures Eddie Copeland and Brian Gillen – were also released unconditionally on Thursday night.
A woman who had been arrested has also been released unconditionally.
Mr Adams said: “The unconditional release of Bobby Storey underlines the contrived nature of the current crisis in the political institutions in the north.
“I want to reiterate my grave concern about the nature in which the murder of two men has been exploited and also at the way the current difficulties have developed in the last few weeks, including the arrest of Bobby Storey.”
Mr Storey’s solicitor John Finucane posted a message on the website Twitter, which read: “After 2 days in Antrim my client Bobby Storey has been freed.
“No evidence was put at any stage & my client will be suing for unlawful arrest.”
Mr Storey is a former IRA prisoner.