The Sinn Fein president, who played a leading role in the peace process in the troubled British province, has been held for questioning since Wednesday night over the killing of mother-of-10 Jean McConville.
Adams has strongly denied any involvement in her murder, one of the most infamous in the three decades of conflict known as The Troubles, and his arrest has raised political tensions.
Police have until today evening -- 48 hours from the time of his arrest -- to question Adams before they must release him, charge him, or apply to a court for more time.
Yesterday, he said the arrest was a "deliberate attempt" by sections of the police to damage his party ahead of local and European elections later this month.
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Any decision to charge Adams, who has led Sinn Fein since 1983 and is the public face of the movement to end British rule in Northern Ireland, could have huge ramifications.
The republicans and pro-British unionists agreed a peace deal in 1998 and now Sinn Fein share power with the Democratic Unionist Party (DUP) in a devolved government in Belfast.
McConville, a 37-year-old widow, was snatched from her home in west Belfast, becoming one of 17 so-called "disappeared" of the conflict.
The Irish Republican Army (IRA) paramilitary group admitted to her murder in 1999 and four years later her body was found, shot in the back of the head, on a beach.
Her children watched her dragged away but one of them, Michael, said he remained too scared of reprisals to give the names of the attackers to police.