The robbery of the €20m relic is the latest in a series of thefts from churches.
In March, the preserved heart of the patron saint of Dublin, St Laurence O'Toole, was stolen from Christ Church Cathedral.
The relic was stored in a heart-shaped wooden box and secured in a small, square iron cage on the wall of a chapel dedicated to his memory.
Last year, three relics, believed to be fragments of the cross used to crucify Jesus were stolen from Holy Cross Abbey in Co Tipperary.
Gardai recovered them in January.
Also in January, a thief stole the container housing the jawbone of St Brigid from St Brigid's Church in Killester, Dublin.
The reliquary was bolted to the altar. However, it had just been cleaned and so the jawbone was not inside.