A 20-year-old man wearing a motorcycle helmet and dressed in all black walked into a busy New Jersey mall minutes before it closed Monday night and began shooting, sending terrified customers running and trapping hundreds more in the building overnight as police searched for him.

Hours later, he was found dead of an apparent self-inflicted gunshot wound in a remote area of the building, officials said Tuesday morning. His brother spoke outside the family's home later and said it was all "an act of self-indulgence."

No one was injured in the gunfire at Westfield Garden State Plaza Mall in Paramus, and authorities said there was evidence to suggest the gunman, identified as Richard Shoop, never had any intention of shooting anyone.

Shoop fired six rounds, striking an elevator, escalator and several store facades along a 300-yard path at about 9:30 p.m. Monday. He was using a Sig Sauer rifle modified to look like an AK-47 that he stole from his brother earlier in the day, officials said.

Paramus Mayor Richard LaBarbiera said he was told that Shoop said to people in the mall "don't worry, just get out of the way."

"And the strong belief is that he had zero intention of bringing harm to anybody but himself," the mayor said.

Bergen County Prosecutor John Molinelli said his motives weren't clear.

"I don't know as I stand here whether his motive was to injure anyone," Molinelli said. "I do not believe that Mr. Shoop thought he was going to come out of here alive."

Officials said Shoop came in from a parking garage and took an elevator to the first floor, where he entered the mall and began to fire.

Shoppers described the confusion and terror as he marched through the shopping center. Customers and workers hid as they heard the gunfire.

"He looked directly in the store and strolled past," said Claire Forbes, who works in a Talbots store. "It was very, very terrifying."

Forbes said the gunman fired as he continued to walk toward the Nordstrom department store.

"There were so many thoughts going through my head. I was so scared."

Johnny Jimenez was getting his phone fixed at an AT&T store when he and other shoppers inside heard the gunshots.

"The first shot fired, we didn't even react to it," said Jimenez, a Navy veteran. "We didn't put two and two together."

He and other shoppers hid in the back of the store.

More than 500 police officers searched the building for hours Monday night before finding Shoop dead.

Meanwhile, police also searched his family's home about 4 miles away, where they found a note. Now authorities are working with relatives to figure out why he killed himself. Officials said Shoop was a drug user.

His brother, Kevin Shoop, said the family was stunned by something they didn't see coming.

"We are not sure what caused him to do this and we are all devastated," he said.

Robert Gega, the owner of a Paramus pizzeria where Shoop had worked for four years, said Tuesday that he had not shown up for his shifts on Friday and Saturday.

Gega described Shoop as a diligent worker and "genuinely very nice."

A family friend described him as a "sweet kid."

"I don't know what went wrong," the family friend said.

The mall was closed Tuesday, but was to reopen Wednesday.

Westfield Garden State Plaza is located at the intersection of Route 4 and Route 17 near the Garden State Parkway. Built in 1957, it was one of the first major suburban shopping malls in the country.

--Brian Thompson contributed to this report.