When David N. Anderson carried out a deadly anti-Semitic terror attack with his girlfriend in a kosher deli in New Jersey last week, he had a phone number and an address written on a note tucked into his back pocket.

The note, which the police found during their investigation, led them to a pawnshop almost 40 miles south of Jersey City, the site of the shooting. On Friday evening, they searched the store and found 10 guns and over 400 rounds of ammunition. The shop’s owner, Ahmed A-Hady, 35, was arrested early on Saturday morning on criminal weapons charges, federal authorities said.

Later on Saturday, according to officials, federal authorities recovered a white van 11 miles from Jersey City, which they believe may be connected to Mr. Anderson and his girlfriend, Francine Graham, who participated in the attack.

The developments came as New Jersey residents continued to grapple with the deadly rampage last week that left four people dead and turned a quiet city street into the scene of a prolonged firefight.

The sequence of events began on Tuesday morning, when Mr. Anderson, 47, and Ms. Graham, 50, killed a police officer in a cemetery in the area who had approached a U-Haul van — not the same van as the white one that was later recovered — that the couple had been driving.

After shooting the officer, Detective Joe Seals, the couple then drove to the JC Kosher Supermarket, where they unleashed a fusillade, killing one of the store owners, a customer and a market employee.

A firefight ensued between the couple and law enforcement officers from Jersey City, New York City, the state police and the F.B.I. At around 3:25 p.m., a police armored vehicle rammed into the front of the store. After more gunfire, officers entered the market, and Mr. Anderson and Ms. Graham were found dead.

Officials have determined that Mr. Anderson and Ms. Graham, followers of the ideology of the Black Hebrew Israelites, an extremist sect that espouses anti-Semitism, had targeted the market. F.B.I. officials have called the attack an act of domestic terrorism.

Officials have not yet made public what connection Mr. A-Hady, who the authorities say, was convicted in 2012 of trying to obtain a controlled dangerous substance, had to the Jersey City shooting, other than that his address in Keyport, N.J., and phone number were on Mr. Anderson’s note.

The search on Friday night at Mr. A-Hady’s pawnshop and home yielded six rifles, three handguns and one shotgun, in addition to the ammunition rounds, including hollow point bullets, which expand when they hit a target, according to officials. Three of the weapons were AR-15 style assault rifles, the same type of firearm used in the Sandy Hook, Las Vegas and Parkland mass shootings. As a result of his 2012 conviction, Mr. A-Hady was not permitted to have any weapons.

He is expected to appear in federal court on Monday.

Over the last week, community members have mourned three of the attack’s victims: Leah Mindel Ferencz, who co-owned the kosher deli with her husband; Moshe Deutsch, a 24-year-old rabbinical student; and Douglas Miguel Rodriguez, a deli employee. A wake will be held for Detective Seals on Monday in Jersey City.

The services have reflected the anger and anguish that swept through Jersey City in the aftermath of the attack. But speaking to mourners at a funeral home on Saturday evening, Mr. Rodriguez’s wife, Martha Freire Carrasco, offered a message of compassion.

“I forgave who did this to my husband,” she said. “I forgave them because if I have hate in my heart, this, what I’m going through would be worse.”

An immigrant from Ecuador, Mr. Rodriguez has been described by friends and family as a hard worker and devoted father. He knew his customers by name and would memorize their children’s favorite snacks so he could place an order before the shop ran out of them, Ms. Freire said.

“I love my father with all my heart and I miss him,” said Amy Rodriguez, his 11-year-old daughter, when she came to the podium. “I want to thank God for all the years he gave me with him. I will always have you in my heart.”

Tracey Tully and Andrea Salcedo contributed reporting.