The suspects - Rodolfo Godinez, 25; his 17-year-old brother, Alexander Alfaro; Jose Lachira Carranza, 29; Melvin Jovel, 19; Shahid Baskerville, 16; and Gerardo Gomez, 16 - were all indicted on murder, attempted murder, robbery and weapons offenses related to the Aug. 4, 2007 killing.
The six men, who have reputed links to the MS-13 street gang, are accused of killing Iofemi Hightower, Terrance Aeriel and Dashon Harvey. The three were college students, and were hanging out behind the Mount Vernon School when they were killed.
Carranza and Baskerville are also charged with sexually assaulting a fourth victim who survived.
The Associated Press usually does not identify victims of rape and is no longer disclosing the woman's name because of the added sexual assault charges.
Essex County Prosecutor Paula Dow said the woman suffered memory lapses from her injuries and is currently in protective custody.
John Dell'Italia, an Orange lawyer representing Carranza, said his client was innocent and would fight the charges. Lawyers for the other defendants did not return telephone messages left at their offices on Monday.
The killings shook Newark and spurred a series of reforms, including adding surveillance cameras in some areas of the city, to penalties for gun owners who fail to report lost or stolen weapons.
Dow said robbery and gang involvement were both elements of the case, but declined to say what police believe to be the primary motive. She also said illegal guns - such as the one used in this crime - continue to plauge Newark streets.
She said the indictments took a year because three of the juvenile suspects had been upgraded to face adult charges, and because multiple agencies had been working together to make sure the case was airtight.
"This is an important case for us, and we're doing it slowly, but we're doing it the right way," Dow said.
If convicted, Dow said the suspects face multiple life sentences.
In the aftermath of the killings, the outcry over Carranza - an illegal immigrant who was out on bail at the time of the murders despite facing separate assault and child rape charges - led to a directive from the state Attorney General that revamped bail policies for illegal immigrants.
The killings also jump-started a project to put surveillance cameras in high-crime neighborhoods in Newark. About $2 million was raised in the weeks after the killings, and the first cameras were in place by September. More than 100 had been installed by the end of June, and police have credited them with cutting down on violent crime.
Last month, the families of the victims filed a lawsuit against the Newark school district that claimed the Mount Vernon School failed to provide adequate security in a rear courtyard where the victims were killed.