The Sinn Féin President says he has grave concerns about the arrest of Bobby Storey.
Mr Storey, the Sinn Fein northern chairman, was detained this morning, along with two other men, in connection with the murder of Kevin McGuigan in Belfast.
At least 13 people have been arrested in relation to the murder of the father of nine so far - all have been released without charge.
Gerry Adams says he accepts the PSNI have a job to do - and stopped short of saying the arrest of Bobby Storey is 'political policing'.
"Sinn Féin didn't kill Kevin McGuigan. In my opinion the IRA didn't kill Kevin McGuigan," Mr Adams said.
"I don't want to go any further than to say I have grave concerns about how all of this has developed, including the arrest of Bobby Storey.
"The PSNI have to be allowed to carry out their investigation, they have to be allowed to conclude their investigation.
Mr Adams added that he would be "shocked if Bobby Storey wasn't released."
The PSNI arrested Mr Storey in connection with the murder of former IRA member Kevin McGuigan in Belfast. He is one of three men - age 59, 58 and 45 - who were detained in the city this morning. The PSNI made the arrests in Derry and then transferred the men to the Serious Crime Suite at Antrim Police Station.
Father of nine Kevin McGuigan was shot dead in Belfast last month and there have so far been 13 arrests in connection with the killing. All have been released without charge.
The PSNI have said they believe some Provisional IRA members were involved in the murder and the fallout has caused political chaos in Northern Ireland.
Earlier, Martin McGuinness said he was "surprised" to learn of the arrest of Sinn Féin chairman for the North, Bobby Storey, in connection with the murder of Kevin McGuigan. He added that the party “look forward with confidence to his early release.”
The deputy first minister said Mr Storey is a “valued member of Sinn Féin's core leadership," who has “played a leading role in the development of Sinn Féin’s peace strategy".
Mr McGuinness described Mr Storey as "a long standing and loyal supporter, defender and advocate of the peace and political processes.
Northern Ireland security correspondent Alan Murray told The Pat Kenny Show that the news of the arrest of Mr Storey "has caused ripples in the political circles here and obviously it’s raising a lot of comments bout the alleged involvement of these people in the McGuigan murder."
