Top secret interviews with convicted Old Bailey car bomber Dolours Price have been handed over to detectives, police confirmed.
The Police Service of Northern Ireland (PSNI) said two detectives from serious crime branch have travelled to Boston to take possession of materials authorised by the United States Supreme Court as part of their investigation into the murder of Mrs McConville.
"The officers will return to Northern Ireland to assess the material and continue with their inquiries," a spokesman added.
Price, who died in January, was an unrepentant republican hard-liner who became a bitter critic of Sinn Fein when the party endorsed the Good Friday Agreement and encouraged the IRA to give up its weapons. She clashed with party leader Gerry Adams in recent years over her allegations that he had been her IRA Officer Commanding during the early 1970s.
The 62-year-old consistently claimed that Mr Adams, now a Louth TD, had ordered the kidnap and killing of Mrs McConville in 1972.
The Catholic mother-of-10 was among dozens of people - later known as the Disappeared - who were abducted, murdered and secretly buried by republican militants during the Troubles. Mr Adams has always denied being a member of the IRA.
Price said she had made the claims in an interview with the American university academics who have compiled an oral history on Northern Ireland's 40-year conflict. The recordings were started in 2001 and were made on the condition that confidentiality would be guaranteed until after the death of the republican and loyalist paramilitaries who took part.
But researchers at Boston College last year lost a Supreme Court challenge in the States when they tried to try and block the release of the tapes after the PSNI launched a high profile legal challenge to obtain the testimony.
Price, the former wife of actor Stephen Rea, was convicted and jailed along with her sister Marian for the 1973 attack on London's Old Bailey courts in which one man died and more than 200 people were injured. She spent eight years in jail including several weeks on hunger strike before being released in 1980.