The men, whom police have not identified, have not been charged with the killings or shootings but were being held on miscellaneous charges.
A white Infiniti SUV believed to be the vehicle seen at the site of the attacks was found Saturday, McCarthy said. He did not confirm reports that the SUV was found at the Jersey Gardens Mall in Elizabeth.
An official familiar with the investigation said the shootings appear to be targeted attacks, not random. The official spoke only on condition of anonymity because the official was not authorized to speak about the investigation.
The attacks occurred Friday afternoon during a 45-minute period in at least three different locations - one a half-block from a middle school. On Saturday a small group of residents staged a march in that neighborhood in honor of the victims.
A 21-year-old man and 24-year-old woman were killed in Friday's shootings. A 27-year-old man was shot in the elbow. Police initially suspected that the shooting of a 16-year-old boy was also connected, but McCarthy said Saturday that ballistics evidence appeared to confirm that the shooting was unrelated.
Police said the white Infiniti SUV was seen at several of the shooting scenes, and at least one surveillance camera captured still photos of the suspect vehicle.
Friday's killings brought more unwanted attention to Newark, a city that is struggling to shed a reputation for gun violence.
In the 14 months since three college-bound friends were slain execution-style in a school playground, numerous anti-crime initiatives have been implemented, notably a network of more than 100 surveillance cameras in high-crime areas.
However, a gunshot detection system that will alert police to the location of gunfire and provide information on the number of shooters and number of shots has not been activated.
Mayor Cory A. Booker praised the surveillance camera system for providing images of the vehicle involved in Friday's shootings.
"They were absolutely helpful to the investigation. Those cameras made a difference in the case," Booker told The Associated Press on Saturday. "Unfortunately, the gunshot detection system has not been operational. When we do launch it, it will definitely increase our ability to react and get people on the scene a lot quicker."
Homicides have decreased dramatically in Newark since 2006, when 106 people slain and the Newark Teachers Union paid for several billboards that implored: "HELP WANTED: Stop The Killings In Newark Now!"
Through Friday, 52 homicides had been committed in Newark in 2008 compared to 83 in the same period in 2007, according to the Newark Police Department. But robberies, burglaries and aggravated assaults all were up compared to last year.
"We've made tremendous progress, but we can never mistake progress with success," Booker said. "We haven't reached the success we seek yet. We haven't solved the problem yet."
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