Fr Griffin would have been known to the Crown Forces, as a known republican sympathiser. On the night of 8 September 1920, he was called out to attend Seamus Quirke, a First-Lieutenant in the local IRA after he was shot seven times at the docks.
He also took part in the funeral mass of Michael Walsh of the Old Malt House following his murder on the night of 22 September 1920.
On 14 November, Fr Griffin was lured from the presbytery by British forces. He was taken to Lenaboy Castle where he was questioned. After being interrogated, he was shot through the head and his body was taken away by lorry and buried in an unmarked grave at Cloghscoltia near Barna.
On 20 November, Fr Griffins remains were discovered by a local man, William Duffy while he was attending cattle.
On 22 November, Crozier travelled to Galway, found that Fr. Griffin had been murdered by his men, and that a plot was afoot to murder Dr Fogarty, Bishop of Killaloe. Crozier writes in Ireland For Ever:
‘I found out that the military inquiry into the murder of Father Griffin (held in lieu of an inquest) was fast with a ‘frame up’ and that a verdict of murder against persons, or somebody ‘unknown’ would result. I told the military commander this and the name of the real murderer, but was informed that a senior official of Dublin Castle had been to Galway in front of me to give instructions as to ‘procedure’ in this murder investigation. At Killaloe next day I received further evidence that the hidden hand was still at work, and was told in confidence that instructions had been received to kill Dr Fogarty, Roman Catholic Bishop of Killaloe, by drowning him in a sack from the bridge over the River Shannon, so as to run no further risk of detection by having his body found.’
On 23 November, Fr Griffin’s funeral mass at St Joseph’s Church, Presentation Road, funeral cortege moved through the streets of Galway, with three bishops, 150 priests and in excess of 12,000 mourners participated. The priest was buried in the grounds of Loughrea Cathedral. A group of enthusiasts gathered together in Galway in the spring of 1948 to form a football club and they decided unanimously to name the club “Father Griffins” and they would grow and flourish to be a major force in Galway football. There is also a road in Galway City called ‘Father Griffin Road’.