Speaking on the anniversary of the murder, Mr Adams said: “In recent weeks there has been considerable focus on the issue of the Dublin and Monaghan bombs and the role of British security agencies in those attacks.
“Collusion between British state forces and unionist paramilitary organisations took many forms. Sometimes it was structured, institutionalised and a matter of British government policy and administrative practice and other times it was informal, opportunistic and sectarian.
“One of its victims was Sinn Féin Councillor Eddie Fullerton who was shot and killed in his home 20 years ago today.
“I knew Eddie well. He was a very popular figure and elected representative in Buncrana. He was a dedicated republican activist who worked tirelessly as a councillor.
“The investigation carried out by the Gardai at the time was inadequate and Sinn Féin supports the family’s demand an independent public inquiry into Eddie’s murder.”
Mr Fullerton was shot by the UFF/UDA, whose leaders were being run at the time by the British Army’s secretive Force Research Unit and RUC Special Branch.
At the time documents containing republicans’ details were regularly handed over to loyalist hit squads by members of the security forces.
As well as running agents inside loyalist groups, the Force Research Unit also had paid agents inside the Gardai.