– Gerry Adams, the leader of the Northern Irish political party Sinn Fein, was released from police custody without charge Sunday after four days of questioning into a gruesome 1972 Irish Republican Army murder of a widow with 10 children. But the police will hand over a file of potential evidence against him to British prosecutors, police officials said.

Adams, 65, turned himself in for questioning Wednesday and was arrested; his detention was extended for 48 hours by a judge.

The police are working on allegations made in the testimonies of Irish Republican Army dissidents, now dead, that were handed over under subpoena by Boston College, which had collected them.

Adams has been accused over the years of membership in the IRA and of being the group’s commander in Belfast; he was accused in these testimonies of ordering the abduction, murder and burial in 1972 of Jean McConville, a widow and mother of 10, who was suspected of being an informer for the British army. Her body was found in 2003, and the police considered hers a “cold case” until the testimonies emerged.

Adams denies all the accusations. And though he has long been the leader of Sinn Fein, once the IRA’s political wing and now a prominent political party, he has never admitted to membership in the IRA, unlike his deputy, Martin McGuinness.

Prosecutors could prosecute Adams later, even just on charges of being an IRA member. But that charge alone after so many years would be widely seen by Sinn Fein and its allies as political interference.

Adams, a former member of the British Parliament from West Belfast and a current member of the Irish Parliament, the Dail, from County Louth, has led Sinn Fein since 1983. The party is running well in the Irish Republic ahead of elections later this month for local councils and for the European Parliament.

The police and officials from Britain, Northern Ireland and Ireland have all rejected accusations from Sinn Fein and McGuinness that the arrest of Adams was political in nature and stemmed from a “dark side” of the current Police Service of Northern Ireland.

Unusually on Sunday, a Sinn Fein junior minister, Gerry Kelly, was allowed into the police station to visit Adams. Kelly, a former member of the IRA, said that Adams believed that his detention was politically motivated.