Published Saturday, 03 May 2014
The protest calling for his release took place at the International Wall on the Falls Road on Saturday afternoon, where a new mural depicting Mr Adams as a "peacemaker, a leader (and) a visionary" was also unveiled.
The former West Belfast MP spent a fourth night in custody at Antrim Serious Crime Suite where he presented himself on Wednesday.
He is being held under the Terrorism Act.
Police had until 8pm on Friday to question the 65-year-old but, following a court bid, they were given until Sunday evening to interview the Louth TD.
Mr McGuinness has condemned the timing of the arrest ahead of upcoming elections as a "political" move by a "small cabal in the PSNI" who have a "negative and destructive agenda to both the peace process and to Sinn Féin".
On Saturday, he also accused police of "deliberately and cynically exploiting the awful killing of Jean McConville and the grief and hurt of her family."
"Our sympathy is with the McConville family," he told the crowd.
The Sinn Féin MLA said some members of the police service are against the peace process.
"No police force anywhere in the world is immune from criticism if it is acting in a politically biased and partisan fashion," he told the crowd.
"The arrest of Gerry Adams is evidence of that fact that there is an element in the PSNI who are against the peace process and hate Gerry Adams and hate Sinn Féin."
"These people want to settle old scores whatever the political cost," he said.
First Minister Peter Robinson, Justice Minister David Ford and Northern Ireland Secretary Theresa Villiers have defended the police's handling of the arrest and denied it was politically motivated.
Mrs McConville was aged 37 when she was interrogated, shot in the back of the head and then secretly buried - becoming one of the so-called "Disappeared" victims of the Troubles.
Her body was not found until 2003 on a beach in Co Louth, 50 miles from her home.
A veteran republican - 77-year-old Ivor Bell - was charged in March with aiding and abetting the murder and five others have been detained and questioned.
The recent police activity followed a decision by a US court compelling a Boston university to hand over to the PSNI recorded interviews with republicans about Mrs McConville's murder.
Mr Adams has always strenuously denied allegations levelled by former republican colleagues that he had any involvement in the murder of Mrs McConville, who was wrongly suspected of being an informer for the British Army.
© UTV News