The night before he was to give his younger daughter a birthday party, Police Officer William C. Johnson went out for pizza and never came home. He died early Friday, apparently a random victim of a drive-by shooting.

Someone fired five or six shots into Texas Fried Chicken and Pizza on Thursday night, blowing out the front window, gouging bullet holes into walls, injuring two people and mortally wounding Officer Johnson, a single father of two who was off duty.

The police said that none of the three victims was the intended target, making this the sort of sudden, unexplained violence that has long been a scourge of this city.

A 19-year-old Newark man described as “a person of interest” in the case was arrested late Friday afternoon.

The shooting comes at a difficult time for the Newark Police Department and Mayor Cory A. Booker. The city laid off about 13 percent of its officers last fall. In recent weeks, Garry McCarthy, the Newark police director, left to lead the Chicago police, and federal authorities announced that they were investigating whether the Newark department had a pattern of mistreating citizens.

Mr. Booker took office in 2006 vowing to fight crime and restore trust in the department, and in his first two years, crime declined. But the murder rate rose in 2009 and 2010, defying a national decline. Crime has continued to rise this year.

“We all feel grievously wounded and harmed,” Mr. Booker said at a news conference on Friday about the slaying of Officer Johnson, a Newark native. “He was one of our own. He’s up from the bricks.”

“Do not misunderstand,” the mayor added. “We will find those people responsible for killing one of our officers. We will not let this cop killer stay on the streets.”

Carolyn A. Murray, the acting Essex County prosecutor, said that the young man who was arrested, Rasul McNeil-Thomas, faced charges in the carjacking of the vehicle that the police believe was used in the shooting, and gun possession charges, but so far has not been charged in the shooting. Officials said they were still looking for another person possibly connected to the shooting.

Officer Johnson, 45, worked in the department’s video surveillance unit, watching the streams of images from security cameras posted around the city. It may be just such cameras that help catch whoever killed him; police officials said they had the video recording from a camera at Texas Fried Chicken and Pizza, and were collecting others from neighboring businesses. The restaurant, at 250 Lyons Avenue, is a short drive from the quiet street where Officer Johnson lived, in the South Ward, near Beth Israel Medical Center. “He would come here every three days,” usually to pick up a pepperoni pie, said Adrees Nahiam, a cashier at the restaurant. “He was a really nice guy.”

Neighbors and patrons say that the restaurant, which stays open until 2 a.m., is a magnet for rowdy teenagers and young men, who are not usually shooed away, and that surrounding area has had a number of violent episodes in the past year.

“A lot of kids hang out in there,” said one neighbor, Kim Baker, 46. “It’s not that bad, but it has its moments.”

At 9:50 p.m. on Thursday, Officer Johnson was standing at the counter, apparently waiting for his order, according to officials who have watched the surveillance video.

Samuel DeMaio, the acting police director, said a vehicle pulled up in front of the restaurant with what appeared to be two people in it, and someone opened fire on the customers inside. Witnesses said five or six shots were fired, sending people in and around the restaurant scattering for cover.

Officer Johnson and a 21-year-old man were both struck in the torso, and taken to University Hospital. Officer Johnson died at 3:10 a.m., Ms. Murray, the prosecutor, said.

The other man, whose name was not released, was in stable condition Friday.

Another bullet struck the shoulder of a 19-year-old woman, a regular customer who was there with a toddler. The woman, whose name the police also withheld, fled on foot with the child, leaving her stroller behind in the restaurant. She reached Beth Israel, where she was treated and released.

In addition to his job with the Police Department, where he had worked for 16 years, Officer Johnson worked part time as a security guard at a Newark apartment complex. He lived in a modest house with his daughters — one just out of college and one in fifth grade.

By all accounts, Officer Johnson doted on the younger girl. “He was going to give her a birthday party today, and now what is that little girl going to do?” Shalonda Coleman, who lives on the next block, said on Friday.

Shakeema Brown, another neighbor, said the girl often told people, “My dad really cares about me; he really loves me.” People up and down the street said that despite a certain reserve, Officer Johnson was always helping neighbors, whether carrying packages or looking after their houses when they were away.

“He would always tell people, ‘Anywhere you go, you’ve got to watch your back,’ ” said Cheryl Newby, whose granddaughter often plays with Officer Johnson’s younger daughter.

He walked nearly every day to the Quality Mini Mart, two blocks from his house for food, toiletries, cigarettes or pipe tobacco, with a “Good evening, ladies” for the group of women he usually passed, chatting on a nearby porch. Often, he would take his younger daughter with him, walking hand in hand, to buy her snacks.

At Garden Towers, the apartment complex where Officer Johnson was a guard, Tyrell Lindsey recalled Officer Johnson reuniting lost children with their parents, and helping elderly residents buy groceries. “He was just a well-loved person,” Mr. Lindsey said.