Luke Wilson is recovering from his injuries at St James' Hospital after he was targeted by a gunman on Sunday afternoon in Dublin's Memorial Park.
Ballyfermot youth Wilson -- who is well known to gardai -- has not made a complaint to officers about the incident.
A source explained: "A forensic link is the important thing in this case but that has not yet been established so the man in custody had to be released.
"But the investigation is ongoing and charges certainly cannot be ruled out in this case."
It has emerged that Luke was targeted because of a pub fight the previous weekend which developed when one of his associates started slagging him about his murdered uncle John.
Sources say the row between Luke and the other man may have kicked off over "a minor debt" but turned violent when the other man started verbally abusing his uncle John.
The pub assault victim is not suspected in Sunday's shooting but one of his best friends is the teenager who was arrested.
In a separate incident, low level criminal David Rice (24) is also recovering from his injuries at Connolly Hospital, Blanchardstown, after he survived 9mm bullet wounds to his head and upper body
Rice had initially told gardai that he had been shot with a pellet gun.
He was attacked as he walked through Fortlawn Park in Blanchardstown, west Dublin, on Monday night.
Rice told gardai his lone attacker was masked but was unable to give a description.