A Peruvian national in the U.S. illegally and who was previously charged with raping a 5-year-old girl pleaded not guilty Friday in the execution-style slayings of three young college students, a day after he surrendered to the Newark mayor.

Jose Carranza, 28, aka Jose La Chira, entered his plea before Essex County Superior Court Judge Michael Casale. A second suspect, a 15-year-old boy, has been held pending a detention hearing, and authorities said more arrests were "imminent."

Carranza, of Peru, was being held on $1 million bail. He turned himself in to Newark Mayor Cory Booker after his fingerprints were lifted from a bottle in connection with the shootings of four college students on Saturday. Three were killed but a fourth survived and was hospitalized after the shootings in a Newark schoolyard.

FOX News has learned Carranza, who has a fake Social Security number, had been arrested on charges of raping a 5-year-old girl and then threatening the child and her parents. In that case he faced a 31-count indictment.

In another, he was arrested on assault charges stemming from a bar fight.

Immigration officials apparently were aware of Carranza's illegal status since his prior arrests, according to Essex County Sheriff Armando Fontoura.

Relatives of the victims embraced each other as they entered to watch the hearing.

Carranza's attorney, Felix Montalvo, called Booker on Thursday to arrange his surrender.

“He said, ‘Mr. Mayor, we’d like him to be turned in directly to you,’” Booker said Montalvo, who also is a close friend, told him.

On Wednesday night, police arrested the 15-year-old boy who along with Carranza is accused of murder, attempted murder, robbery, weapons offenses and conspiracy to commit the crime of robbery, Essex County Prosecutor Paula Dow said. Authorities were seeking to have the minor tried as an adult.

Dow said she doesn't believe there is any familial relationship between the two in custody.

The teen, who is Hispanic, is an American citizen with a Newark address, Booker said.

“I don’t think words can describe the level of emotion I feel,” he said of the crimes.

“We will confirm that there are others we are looking for," he said, adding, "I am confident all the suspects in this investigation will be apprehended."

Carranza's attorney, Montalvo, led him by the hand during his surrender.

“He simply came forward," Booker said. "He said nothing. We put him in handcuffs."

The sole survivor of Saturday night's shootings, 19-year-old Natasha Aeriel, provided information from her hospital bed after being shot in the head.

Aeriel was with her brother, Terrance Aeriel, 18; Dashon Harvey, 20; and Iofemi Hightower, 20, who were forced to kneel against a wall and were shot execution-style outside a Newark school.

The students had been planning to attend Delaware State University.

The Associated Press contributed to this report.