NEWARK, N.J. &

Police arrested a 15-year-old boy in the killings of three college students in a schoolyard, shootings considered jarring even in a city used to violence, a law enforcement official said today.

The teen was arrested Wednesday night, and an arrest warrant was issued for 31-year-old man, Mayor Cory A. Booker said.

Four friends, ages 18 to 20, were shot while hanging out in a school yard Saturday night. Authorities have said robbery appeared to be the motive.

Three of the victims &

Terrance Aeriel, 18, Dashon Harvey, 20; and Iofemi Hightower, 20 &

were forced to kneel against a wall and were shot at close range. The fourth, 19-year-old Natasha Aeriel, Terrance Aeriel's sister, survived a wound to her head and is hospitalized.

Authorities were seeking a man named Jose Carranza based on fingerprint and ballistics evidence, Booker said. The teen's name was not released because of his age.

Despite being under sedation for periods, Natasha Aeriel has been providing authorities with information about the shootings, the mayor said.

The killings brought unwanted publicity to the city, which has struggled for years with violent crime. Residents and law enforcement organizations have donated $150,000 to aid the victims' families and to a reward fund.

"This is a defining moment for our city. The crime is not going to define Newark but our response to it," Booker said Thursday on ABC's "Good Morning America."

All four victims were planning to attend Delaware State University this fall. Instead, three were to be buried Saturday in separate services.

A friend of the victims, Samantha Williams, said she was overwhelmed by news of an arrest.

"I can actually stop crying, I can sleep peacefully," said Williams, 18, of Orange.