Fr Damien Ryan told mourners at the Holy Family Church in Southill that when he served in the parish, David was one of the altar boys.
Fr Ryan said: “He was a lovely young lad with a twinkle in his eye. It is just so sad this has happened. Young people growing up and to die in such dreadful circumstances.”
It emerged yesterday that Mr Nunan was hit by at least two bullets.
One theory is that he fell foul of a local drugs gang.
He died instantly in the fatal attack carried out in a laneway at Parteen village, four miles from the city in the early hours of Friday.
He had a criminal record, mostly for driving offences, and was only released from prison on Monday of last week.
His body was discovered last Friday morning at around 8.30am.
Mr Nunan, 25, was last seen alive by family members when he left his home in Southill at around 1am on Friday. Post-mortem results showed he died at around 2.30am.
Garda sub aqua divers have been searching the tail-race of the ESB power station in nearby Ardnacrusha for the handgun used in the murder.
It is believed Mr Nunan left home after receiving a call on his mobile phone.
He was driven to Parteen where a gunman may have lay in wait in the laneway or the person he travelled with pulled a gun and shot him.
His mother Mary, and sisters Nicole and Sinead were the principal mourners at the Requiem Mass at the Holy Family Church in Southill yesterday. Ms Nunan lost her only other son in a domestic accident when David was just seven.
The burial took place at Mount St Oliver cemetery.
Meanwhile, house-to-house enquiries were still being carried out.
Members of the Garda Bureau of Criminal Investigation have been called in to join in the investigation with detectives from Henry Street and Mayorstone stations.