Martin Conmey was one of three local men accused of killing Úna Lynskey (19) who disappeared near Ratoath, Co Meath, in 1971.
The men claimed they were subjected to brutal interrogation by some garda detectives, allegations that were strongly denied by the investigators involved.
Mr Conmey was convicted of manslaughter in 1972 and served three years in prison, but this was successfully appealed in 2010.
The Court of Appeal later ruled in 2014 that Martin Conmey’s conviction was a miscarriage of justice.
It has now emerged that Garda chief Drew Harris has written to him in recent weeks and offered an apology.
Mr Harris has also ordered the Garda’s Serious Crime Review Team to review the relevant investigation regarding the suspected murder of Úna Lynskey.
The teenager went missing in October 1971 and her body was discovered two months later near the Dublin Mountains.
The case will feature tonight on RTÉ One as part of a new documentary series
Crimes and Confessions
The families of the other two men wrongly accused – Dick Donnelly and Martin Kerrigan – have yet to receive a State or Garda apology and are calling for an inquiry into the investigation.
Mr Donnelly was convicted of the manslaughter but won an appeal against his conviction in 1973.
Before Mr Kerrigan could stand trial he was abducted and killed by Ms Lynskey’s brothers Sean and James, and her cousin John Gaughan. They were later convicted of his manslaughter.
A Garda spokesman said that the outcome of the cold case unit’s review “will determine whether further action is required from An Garda Síochána”.
The spokesman added that “in general, in circumstances where a review of an investigation has taken place and this reveals it is appropriate, then an apology to an individual or individuals will be made”.
In 2014, the Court of Criminal Appeal strongly criticised the conduct of the Garda investigation in the case.
Crimes and Confessions, a new three-part series, airs tonight on RTÉ One at 9.35pm.