He can't be named because of his age. Two weeks after the shooting, Keith Hall (23), of Kilmartin Drive in Tallaght, was charged with murder.
On the night of Melanie's killing, a black SUV pulled up alongside a car that Melanie had been sitting in with Christy Moran and other pals and a gunman opened fire.
Hall has already been charged with possession of a double-barrel, sawn-off shotgun with intent to commit an indictable offence.
Melanie, a member of the Travelling community, was laid to rest after a funeral service in north London.
She became the youngest victim of gun violence on Dublin's streets and her death was seen as a new low in criminality.
A family member today said they were too upset to talk. "Nothing will bring Melanie back," they added.
At her funeral in the historic St Dominic's Priory in Kentish Town, Melanie's father Shaky described her as "the greatest love of all" as she was laid to rest.
Brought to her final resting place in a white carriage drawn by four white horses wearing pink plumes, Melanie was buried in a pastel pink casket, dressed in a pink tracksuit.
Melanie's parents, Shaky and Melissa, as well as Christopher's father Michael, were embraced by mourners as they joined the convoy of a pink taxi, the horse-drawn carriage, a white limousine and a truck bearing the floral tributes.
At the funeral mass, the mourners were told how Melanie had grown up in the Camden borough and made her communion in the same church her funeral was held at.
"She had longed to be a bride. She was full of life, and the photographs we see here today show how vibrant Melanie was," said the priest.
Mourners heard how Melanie's life was taken "so suddenly, needlessly and pointlessly".