NEWARK, New Jersey (CNN) -- A third suspect was arrested in connection with the execution-style slayings of three college students in a schoolyard, Newark Mayor Cory Booker said Friday night.
That suspect, identified as a 15-year-old male by officials, was arrested earlier Friday. Additional arrests are likely to be made soon, officials said.
The crime shocked residents of Newark, New Jersey, galvanizing them to express their outrage at the city's street violence.
Earlier Friday, an undocumented immigrant pleaded not guilty to murder and other charges. Watch a shackled Carranza in court »
Jose Carranza, 28, was being held on $1 million bond.
Another 15-year-old was arraigned on Thursday and pleaded not guilty in a closed hearing.
County Prosecutor Paula Dow said she wants the teen tried as an adult.
Carranza and the teen are charged with three counts of murder, four counts of first degree robbery, one count of attempted murder, various weapons offenses and one count of conspiracy to commit the act of robbery, prosecutors said.
Booker said there was no indication of gang or narcotics activity in connection with the slayings.
Wearing an orange jail jumpsuit, Carranza spoke softly through a translator. He had surrendered Thursday to Booker, who attended the arraignment.
"He knew maybe if he turned himself in to me he would be safer, but my focus was to get him off the streets," Booker said Friday morning during an appearance on CNN's "American Morning."
Carranza had been using a bogus Social Security number, Sheriff Armando Fontoura said. Carranza is an undocumented immigrant from Peru, his lawyer acknowledged in court.
Carranza had been scheduled to appear in court Monday to answer two previous indictments. One accuses him of sexually assaulting and threatening to kill a 13-year-old, a girlfriend's child. Another charges him with an array of assault and weapons offenses.
Police earlier said they were looking for two juveniles and one adult who may have been involved in the shootings, Newark's daily newspaper, The Star Ledger, reported in its Friday editions. Fontoura confirmed to CNN that was the "ballpark" age range of those being sought.
Newark Police Director Garry McCarthy said his office was "close to piecing the entirety of this event together."
Ballistics evidence, information from the shooting's lone survivor and a fingerprint lifted from a beer bottle at the scene led to the major break in a case that has outraged a city numbed by street violence.
"There seems to be no motivation, no provocation," Booker said, calling the crime "evil."
"This was just a disgusting, vicious attack and it's troubling," Booker said. "What they were attacking, [was] not only these amazing children and their families but what the core of Newark is really about."
Prosecutor Dow downplayed any racial motive.
"We are pursuing this as a horrendous robbery that went terribly wrong," she said. "The mayor has made clear that given the great diversity of this city and the large influx of all nationalities, we, as a people, need to come together and not make race an issue. Here, it certainly is not."
The first break in the case came when the first teenager was taken into custody at about 11 p.m. Wednesday.
Much of the information that authorities have collected has come from the lone survivor of the attacks, Natasha Aeriel, 19.
"She's been incredibly helpful," McCarthy said. "There have been identifications made, and she's been of great assistance to us at this point, in spite of her condition, which fortunately is improving daily."
Aeriel is under heavy guard at a hospital, where she is recovering from gunshot and knife wounds.
Authorities have asked for the public's help in the rapidly developing case. A $150,000 reward is being offered for information.
Newark has become accustomed to violence but the slayings on Saturday night touched a nerve.
The four friends, ages 18 to 20, were shot while listening to music at the schoolyard.
Three of them -- Terrance Aeriel, 18, Dashon Harvey, 20; and Iofemi Hightower, 20 -- were forced to kneel against a wall and were shot in the head, execution style.
Authorities have said robbery appeared to be the motive.
While Newark has seen 60 homicides this year, the schoolyard killings stood out because the victims, by all accounts, were good kids. All four were enrolled at Delaware State University or were in the process of enrolling. E-mail to a friend
CNN's Janine Brady contributed to this report