A tape recording of a deceased Belfast IRA commander in which Gerry Adams is accused of ordering the murder and secret burial of a widowed mother of 10 in 1972 will be broadcast for the first time this week.

A former IRA hunger striker, Brendan Hughes, alleges the Sinn Féin president was one of the heads of a unit that kidnapped, killed and buried west Belfast woman Jean McConville. Hughes, who died in 2008, is recorded as saying: "There was only one man who gave that order for that woman to be executed – and that man is now the head of Sinn Féin." Hughes also says that Adams went to the McConville children after their mother was abducted and promised an internal IRA investigation. "That man is the man who gave the order for that woman to be executed. I did not give the order to execute that woman. He did."

Adams is challenged on the BBC's Storyville programme over whether he was a senior Provisionals commander in Belfast at the time McConville was abducted, just before Christmas 1972. "That's not true," Adams replies, adding that he has not "shirked" his own responsibilities in the conflict. The Sinn Féin leader has always insisted that he was never in the IRA.

In response to the tape, Adams, who is the Sinn Féin member for Louth in the Irish parliament, accuses his former friend of lying. "Brendan is telling lies," Adams tells the programme. He adds: "I had no act or part to play in the abduction, killing or burial of Jean McConville or any of the others."

An expert forensic detective tells the joint BBC Northern Ireland-RTE production that the IRA sometimes weighed bodies down with heavy stones to ensure that the corpses would not surface if the bogs they were buried in ever dried up.

Storyville reveals that the first of the "disappeared" to be found back in 1999, north Belfast man Eamon Molloy, had received the last rites from a Catholic priest. The priest saw Molloy tied naked to a bed and asked his captors if any of them had rosary beads that their prisoner could hold when he was to be shot.

Security sources in the Republic told the Observer last week that up to four additional men who were "disappeared" by the IRA have not yet been identified by the organisation set up to find the Troubles' missing victims. The Independent Commission for the Location of Victims' Remains (ICLVR) has so far found eight of the "disappeared", including McConville, but seven on their official list are still unaccounted for.

A spokesman for the ICLVR, Geoff Knupfer, said: "At this moment there is no information to suggest there is any addition to the list." However, security sources insist that at least four IRA victims were buried in secret. The film is to be broadcast on BBC Northern Ireland and RTE on Monday and BBC4 on Tuesday.

It includes a reading of the late Seamus Heaney's poem The Bog Queen, which the Nobel laureate agreed could be used in the programme to remember the plight of the "disappeared".

• This article was amended on 3 November 2013 to correct broadcast dates for the Storyville programme