DUBLIN — Police in Northern Ireland arrested Sinn Fein party leader Gerry Adams on Wednesday over his alleged involvement in the Irish Republican Army’s 1972 abduction, killing and secret burial of a Belfast widow.

Adams, 65, confirmed his own arrest in a prepared statement and described it as a voluntary, prearranged interview.

Police long had been expected to question Adams about the killing of Jean McConville, a 38-year-old mother of 10 whom the IRA killed with a single gunshot to the head as an alleged spy.

According to all authoritative histories of the Sinn Fein-IRA movement, Adams served as an IRA commander for decades, but he has always denied holding any position in the outlawed group.

“I believe that the killing of Jean McConville and the secret burial of her body was wrong and a grievous injustice to her and her family,” Adams said. “Well publicized, malicious allegations have been made against me. I reject these. While I have never disassociated myself from the IRA and I never will, I am innocent of any part in the abduction, killing or burial of Mrs. McConville.”

Reflecting the embarrassment associated with killing a widowed mother, the IRA did not admit the killing until 1999, when it claimed responsibility for nearly a dozen slayings of long-vanished civilians and offered to try to pinpoint their unmarked graves. McConville’s children had been told she abandoned them, and they were divided into different foster homes.

Her remains were discovered only by accident near a Republic of Ireland beach in 2003. The woman’s skull bore a single bullet mark through the back of the skull, and forensics officer determined she’d been shot once through back of the head with a rifle.

Adams was implicated in the killing by two IRA veterans, who gave taped interviews to researchers for a Boston College history archive on the four-decade Northern Ireland conflict. Belfast police waged a two-year legal fight in the United States to acquire the interviews, parts of which already were published after the 2008 death of one IRA interviewee, Brendan Hughes.

Boston College immediately handed over the Hughes tapes. The college and researchers fought unsuccessfully to avoid handover tapes of the second IRA interviewee, Dolours Price, who died last year.

Both Hughes and Price agreed to be interviewed on condition that their contents were kept confidential until their deaths.

In his interviews Hughes, a reputed 1970s deputy to Adams within the Belfast IRA, said McConville was killed on Adams’ orders.

Hughes said Adams oversaw a special IRA unit called “The Unknowns” that was committed to identifying, killing and secretly burying Belfast Catholic civilians suspected of spying on behalf of the police or British Army.