Gerardo Gomez, who was 15 at the time of the slayings, is the youngest of six men and boys charged in the case.
Opening statements are under way in his trial in Superior Court in Newark.
The prosecution told jurors Thursday that they would hear a case of "children killing children, and killing them with shocking violence."
Gomez was waived to adult court and faces life in prison if convicted of murder and felony murder.
Three of the defendants were convicted and two have pleaded guilty. Most were admitted members of the MS-13 street gang.
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