Rodolfo Godinez, a Nicaraguan who was one of six men and boys charged with the brutal slayings, was convicted on all 17 counts. A jury returned the verdict in state Superior Court after nearly four hours of deliberations.
The killings of Dashon Harvey, Iofemi Hightower and Terrance Aeriel spurred a wave of anti-crime measures in Newark.
A fourth victim survived and testified against Godinez. She is not being identified by The Associated Press because of sexual assault charges against two other defendants. All four victims were enrolled or about to be enrolled at Delaware State University.
Family members of the victims wept and rubbed one another's backs quietly as the verdict was read. Earlier, when it was announced the jury had reached a verdict, several of them had gasped and started clapping. The judge warned the gallery to stay calm once the verdict was read.
The three victims were found slumped against a wall of the playground, each having suffered a gunshot wound to the back of the head. Hightower and the survivor also were slashed with a machete.
Without a wealth of physical evidence tying Godinez to the scene - he left DNA on a beer bottle at the playground but wasn't tied to the gun or knife used in the attacks - prosecutors used statements Godinez made to police and to a jailhouse acquaintance that appeared to implicate him.
Before deliberations, state Superior Court Judge Michael Ravin instructed jurors that, under New Jersey's accomplice liability statute, they could find Godinez guilty of the murders even though there was no evidence presented that he pulled the trigger.
Godinez's attorney, Roy Greenman, had argued his client was at the scene but didn't take part in the attacks.
Godinez could face several life terms in prison at sentencing on July 8.
