Twenty two year old William (Liam) Heffernan was employed by the Commercial Hotel, Midleton as a chauffeur. When off duty, the car he drove was often used to convey officers of the local IRA battalion to various locations where they organised and trained outlying units.

On the evening of November 27th, 1920, he and four members of the fourth battalion were in a car which was parked outside a premises then owned by Whites (now Barrys) near the bridge at Castlemartyr. The battalion Vice Commandant had gone to Whites to transact some business.

Two members of the local RIC had visited Cork city that day and returned by train to Mogeely, the nearest station to Castlemartyr. They then cycled back to the village and one of them recognised Liam Heffernan as he sat in the car reading a newspaper. Knowing him to be a member of the IRA, both policemen approached the car and began to question the occupants.

Almost immediately the shooting began. Onlookers claimed that the police constable fired on the occupants without warning, although this has never been confirmed. Upon hearing the gunfire outside, the IRA officer in Whites rushed out and while firing at the police, succeeded in getting into the car. In the exchange of gunfire the constable was killed and the sergeant was also hit.  Liam Heffernan, although seriously wounded, managed to start the car and drive it away. He swung the car sharply over the bridge and onto the Mogeely road but it had not gone far before it became obvious that the driver was dying. One of his companions then took over the wheel and they eventually reached Conna, where the local doctor pronounced Liam Heffernan dead.

The monument to William Heffernan, near the scene of his shooting at Castlemartyr.

His body was taken to the home of his relatives where a wake took place. In the early hours of the morning of Monday November 29th, he was interred in Knockmourne cemetery, where a Celtic cross now marks his grave. An inscribed stone monument to his memory was unveiled in Castlemartyr on Sunday May 23rd, 1971, just a short distance from the place where he was shot.