The former director of Boston College’s archive of IRA and loyalist paramilitary material has made a complaint to Northern Ireland’s police ombudsman over how tapes of testimonies were used in an attempt to launch an unsuccessful prosecution of the Sinn Féin leader, Gerry Adams.

The author and journalist Ed Moloney says the Police Service of Northern Ireland encouraged a member of murder victim Jean McConville’s family to support a case against Adams in return for the tapes, which would later be available for use in any civil action brought against Adams.

On Tuesday the Public Prosecution Service in Belfast confirmed there was insufficient evidence to prosecute Adams and six other people in relation to the killing of McConville, who had 10 children.

In response, some of the murdered widow’s children announced that they would try to pursue Adams in a civil action similar to the groundbreaking case that families of the Omagh bomb massacre victims brought against Real IRA leaders.

The McConville family’s case will be taken up by London-based solicitors McCue & Partners, the same law firm that acted on behalf of the Omagh families.

The evidence that led to Adams’s arrest last year, as well as the other six, was partly based on the Boston College tapes. These were a series of recorded testimonies from IRA and loyalist paramilitary veterans that were to form a historical archive about the armed campaigns of the Troubles. They were only to be released when each of the participants had died.

The PSNI pursued some of the taped interviews – which they claimed contained knowledge of McConville’s disappearance and murder – through the US courts system.

Moloney, who fought a campaign in the US to try to stop the handover of some of the Boston College tapes, has now complained formally to the police ombudsman.

In a statement, the author of The Secret History of the IRA said detectives had told a McConville family member “that if he agreed to make a formal complaint, outlining his belief that the Boston College archive held material relevant to the murder and disappearance of his mother, then the detectives would ensure that at the conclusion of their criminal investigation, the material would be made available to him and other members of his family to do with as they wished.

“In other words the family would be able to launch a civil claim against individuals they believed responsible for their mother’s death, using the interviews obtained from the Boston College archive. Without that complaint, the PSNI investigation would have been stillborn.”

Moloney said the alleged offer to pass on the relevant material about McConville’s abduction, murder and secret burial in December 1972 was a breach of article 7 (2) of the mutual legal assistance treaty between the US and UK.

It states: “The requesting party shall not use or disclose any information or evidence obtained under the treaty for any purposes other than for the proceedings stated in the request without the prior consent of the requested party.”

The former director of Boston College’s Belfast Project said: “At the time that the offer was made by PSNI detectives the disposition of the US government was a complete unknown and so they were in no position to make an offer to hand over any material to the McConville family. In effect, they misled the family member.

“I understand that this transaction is already the subject of a separate complaint to the ombudsman’s office lodged some time ago.”

The killing of McConville, a Protestant who became a Catholic convert, has haunted both Adams and the peace process.

In front of her children, at their home in the Divis flats complex, the west Belfast woman was dragged away by an IRA gang, driven across the border to the Irish Republic, shot in the head at a remote coastal spot in Co Louth, and then buried in secret.

Former IRA members, including Adams’s former friend, the hunger striker Brendan Hughes, alleged in the Boston College archive that the Sinn Féin president had given the order for the widow to be disappeared after she was shot as an informer.

Adams, a member of the Irish parliament for Louth and former Belfast West MP, has consistently denied claims of involvement in the McConville murder or of ever being in the IRA. He said the decision not to proceed with any criminal case against him and the six other people was “long overdue”.