Sinn Fein president Gerry Adams will not be prosecuted in connection with the IRA murder of Belfast widow and mother-of-10 Jean McConville.
Northern Ireland's Public Prosecution Service (PPS) said police evidence against Mr Adams and six others, among them Sinn Fein's northern chairman Bobby Storey, was not strong enough to justify charges.
Mrs McConville's son Michael vowed that the family's four-decade quest for justice would go on, "no matter how long it takes".
None of the four women and three men reported to the PPS by detectives investigating the 1972 killing will face IRA membership charges.
All were arrested last year, with senior prosecutors taking many months to assess the police files.
The evidence against Mr Adams, who has always strongly denied involvement, related to allegations made by former paramilitaries to researchers compiling an oral archive of the Troubles for Boston College, Massachusetts.
Detectives from the Police Service of Northern Ireland (PSNI) seized the tapes in late 2013 after winning a court battle in the US.
Deputy Director of Public Prosecutions Pamela Atchison said: "We have given careful consideration to the evidence currently available in respect of each of the three men and four women reported and have concluded that it is insufficient to provide a reasonable prospect of obtaining a conviction against any of them for a criminal offence."
Mr Adams is on a transatlantic visit to the US and Cuba.
Eleven people were arrested in the case last year. One man - veteran republican Ivor Bell - was charged by detectives within days of his detention.
The 78-year-old from Ramoan Gardens in west Belfast, whose case has not yet reached trial, denies aiding and abetting the murder and IRA membership.
Mrs McConville was dragged screaming from her children in the Divis flats in west Belfast by a gang of up to 12 men and women after being wrongly accused of informing to the security forces.
She was interrogated, shot in the back of the head and then secretly buried, becoming one of the "Disappeared'' victims of the Troubles.
Her body was not found until 2003 when a storm uncovered her remains on a beach in Co Louth in the Irish Republic, 50 miles from her home.
PPS officials outlined the non-prosecution decisions to Michael McConville this morning. The family has the right to appeal.
"Those who ordered, planned and carried out this war crime thought that their guilt could disappear along with her body," said Mr McConville.
"But it has not and we will continue to seek justice for our mother and see those responsible held to account no matter how long it takes."
Mr Adams, 66, a former MP for West Belfast and now an elected representative for Co Louth in the Irish Dail, was arrested and questioned for four days about the murder last April.
He was detained after voluntarily presenting himself for interview at Antrim police station.
After more than 40 years of relative inactivity in the murder investigation, the case was invigorated in late 2013 when detectives obtained the taped recordings of former IRA members talking about the shooting.
Three of the interviewees in the archive made claims about Mr Adams's involvement.
Former IRA commander Brendan Hughes and Old Bailey bomber Dolours Price, both now dead, claimed Mr Adams ordered the killing - allegations the Sinn Fein veteran denied.
On his release last year, Mr Adams said most of the questions posed by detectives related to the claims made on the Boston tapes.
It is understood prosecutors concluded the "hearsay" evidence on the tapes was not of sufficient strength to be relied on in court, as it lacked clarity and much of it was based on inference and speculation.
Bell has been charged on the basis of material recorded for the Boston archive.
The crucial difference with Mr Adams's case is understood to be that the recording detectives are relying on against Bell is alleged to have been made by the defendant himself.
While Bell denies he is the man on the tape, in the eyes of prosecutors it amounts to a confession - a much stronger form of evidence than the hearsay claims against Mr Adams.
Of the seven files reviewed by the PPS over the last number of months all but one related to the events around the murder.
Mr Storey, 59, was questioned as part of the wider police investigation, namely about an alleged IRA internal investigation into the whereabouts of the Disappeared bodies in the 1990s.
Mr Adams and the other man were not alleged to have had direct involvement in the murder itself. In the Sinn Fein leader's case, the police file focused on allegations that he ordered it.
The four women were alleged to have been in Mrs McConville's flat when she was abducted.
Ms Atchison handled the cases as Director of Public Prosecutions Barra McGrory recused himself as he had represented Mr Adams as a lawyer before joining the PPS.