1888 Born from death cert
There are a number of possible MIC cards for him
1920 Dec 22. William Shanahan was taken to Ennis Jail where his interrogation continued. The IRA believed that while being taken to the toilet by Provost Sergeant David Finlay, Shanahan was shot in the head at point blank range by Finlay - O Ruairc in Blood on the Banner makes this assertion. The IRA believed that Shanahan was shot in reprisal for the death of Alan Lendrum. Certainly Willie Shanahan died December 22, 1920 in Military Barracks, Ennis, Co Clare. GRO Jan/Mar 1921, b1895. However it would seem to be a wrong extrapolation of what happened. I would contend that McDonough records that Findlay beat them up, but that does not mean that Findlay fired the fatal shot. The British inquest is quite clear that the shot was fired by CSM W Strath
Tom McDonough Witness Statement. We were brought to the R.I.C. barracks in Ennistymon where we were interrogated and given a few kicks and bashes. We were then removed to the military post in Ennistymon where we were interrogated in a gentlemanly manner by a British officer. A few days later we were removed to Ennis military barracks. There we were savagely attacked by a party of military led by a provost sergeant named Davis Finlay. Finlay was a native of Scotland and he had earned a notorious name for himself in Ennis for his cruelty and for the third degree methods he used on prisoners. When Finlay and his gang were finished with us I would say that Neylon was the worst hurt. He was covered with cuts and bruises; he was bleeding from the scalp and his fingers were damaged when, with his hands, he tried to ward off kicks.”
McDonough was released from Limerick Prison in Aug 1921, he records that some months later " I chanced to be in the Queens Hotel in Ennis one day when Finlay came in. He was in civilian clothes and I am sure I would have scarcely recognised him were it not for the fact that he approached me and wagged his finger at me and said " I know you and you are a so and so, and you are one of the Shinners. I learned that he was then a regular visitor to the hotel bar. I passed this information on, and that night, when Finlay left the hotel, he was met by some of our boys in Ennis who took him down a laneway and administered him such a dose of his own medicine that he died of its effects the following day"
1922 Jan 18. Findlay dies at Ennis Gaol, where the Royal Scots were based. Cause of death is given as Congestion of the Lungs for 7 days and Syncope. The informant is Private John Drysdale
1922 Jan 27 Four hundred of the Royal Scots from Ennis left Dublin.
British soldiers killed in Ireland
The man may have been beaten very badly by one Eamonn Barron and that he died of his injuries. The information contained in your initial query (that Finlay shot Willie Shanahan) is not supported by the records, though some news reports indicated that he was shot by the provost sergeant, so the author of the book that named Finlay can be forgiven for the mistake.