They arrested 25-year-old Nicholas Welch on Monday night at his home, just a few doors away from the off-campus house where the shooting occurred early Saturday. A second man, 19-year-old Marcus Bascus, was still being sought.
Both men were charged with murder, conspiracy and weapons offenses. Police believe Welch was the shooter and that Bascus provided him with the gun, either a .357- or .38-caliber weapon, based on shell casings found at the scene.
Welch was being held on $2 million bail and was expected to make an initial court appearance Tuesday or Wednesday. He "didn't say much of anything" when he was arrested around 9 p.m., Acting Essex County Prosecutor Robert Laurino said at a news conference.
Police said Welch tried to enter the party, was refused admittance and then returned moments later with a gun and started firing. Nineteen-year-old Seton Hall student Jessica Moore, an honors student from Disputanta, Va., who was majoring in psychology, was shot and died later that day.
The injuries to the other four victims weren't considered life-threatening. Two of the injured were 19-year-old women who go to Seton Hall, and one was a 25-year-old man who attends the New Jersey Institute of Technology. The other was a 20-year-old man from New York who is not a student.
Laurino credited a police lockdown of the block after the shooting for helping hasten Welch's arrest.
"He probably stayed in his house because he couldn't leave his house," Laurino said.
It was not known if Welch had retained an attorney.
Meanwhile, more witnesses were being interviewed by police on Monday.
Derel Stroud, 24, said he saw the suspected gunman as he went to the house to pick up two girls to drive them home.
"The girls said they weren't letting anyone else in because it was too packed," said Stroud, who didn't attend the party. "When I pulled up I heard an altercation - I heard yelling and some glass break. I heard someone yell, 'They're fighting! Party's over! Go home!"
Stroud said he then saw a man with a beard walk from the house toward another man standing on the curb. Stroud said he heard the bearded man say, "Give me the burner," which Stroud took as slang for a gun.
With his friends in the car, Stroud said, he sped away but heard two gunshots in the distance. About a block down the street, he saw an East Orange police officer performing a traffic stop. Stroud said he told the officer to go to the house because there was a shooting. He said he also called 911. By the time Stroud circled the block, police cars had surrounded the home, he said.
The party was primarily for students at Seton Hall, a private Catholic university with a gated campus in South Orange, about 15 miles from New York City.
The 10,000-student university, with its collection of red brick buildings tucked behind a wrought-iron fence, stands in stark contrast to the gritty neighborhood where the party was held a mile away.
Stroud said a group of students gathered on campus to watch the news conference on television Monday night and to share their memories of Moore.
"It's a relief," he said of the arrest. "It was scary to think that he (the suspected gunman) was so close by still."