Richard Dekker had denied murdering the teenager
Two men from Dublin 15 will be sentenced next month for their parts in the death of Daniel McAnaspie, who was killed while in State care in 2010.
Last month, Trevor Noone pleaded guilty to his manslaughter - while his co-accused Richard Dekker was today convicted of his murder.
The prosecution never accused Dekker of wielding the garden shears used to kill Mr McAnaspie at Tolka Valley Park in Blanchardstown in February 2010.
But by going along with a ruse to lure him there while knowing his co-accused Noone was armed with a deadly weapon, the jury was clearly satisfied he had aided and abetted and should be convicted of murder.
The court heard Noone decided to give him a hiding for fighting with a relative of his in Finglas.
Dekker told gardaí that Daniel begged for his life, and that he tried to intervene but was afraid he would be next.
Daniel was in the care of the Health Service Executive (HSE) at the time and was reported missing when he failed to show up for a lift home.
His skeletal remains were found in a drain in Co Meath three months later.
His killers will be sentenced next month.