She was being detained at Tullamore Garda Station.
A woman arrested in the Midlands as part of the investigation into the murder of Patrick Heeran has been released without charge.
She was being detained in Tullamore Garda station for questioning along with a man in his mid twenties who remains in custody.
Patrick Heeran disappeared from Mohill,Co.Leitrim in October 2011 - his body was never found.
Gardai say their investigation is still ongoing and a file on the arrests is being prepared for the DPP.
The 48 year old was last seen in Mohill in Leitrim eight years ago.
In 2018, his family made an emotional appeal for information on the TV show "Crime Call", which at the time Gardaí said received a very good response.
Yesterday afternoon, a man in his mid 20s and a woman also in her mid 20s were both arrested in the midlands area and are detained at Tullamore Garda Station.
The man can be held for up to 24 hours.