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.