The driver of the car did not immediately report the shooting to the authorities, said Rabbi Jack Meyer, the president of Misaskim, a nonprofit Jewish organization.

But several days after the Jersey City attack, Mr. Meyer said, the man “put two and two together” and contacted him. The man told Mr. Meyer that he was on his way to work at about 9:45 a.m. when he saw a U-Haul van ahead of him on the highway.

Moments later, Mr. Meyer said, a bullet flew through the driver side window. Mr. Meyer said he had put the man in touch with the authorities.

Ballistics tests showed that the bullet had come from a .22-caliber handgun found in the rental van used by Mr. Anderson and Ms. Graham on Dec. 10, officials said. Cellphone records also indicated that Ms. Graham’s phone was in the area where the highway shooting occurred around the time it happened, officials said.

Officials had previously identified Mr. Anderson and Ms. Graham as the leading suspects in the killing of a taxi driver who was found dead in the trunk of a Lincoln Town Car in Bayonne on Dec. 7, officials said.

On Monday, officials said that ballistics tests had linked the same .22-caliber handgun used in the highway shooting to the death of cabby, who was bludgeoned and shot in the head.

The authorities also tied Mr. Anderson and Ms. Graham to the taxi driver’s killing with other evidence. His blood was on a Bible found in the rental van and his DNA was on clothing found there, officials said.