PHILADELPHIA -- Authorities searched Wednesday for a gunman who halted an FBI convoy towing two cars in a drug investigation and opened fire. Two people were wounded in the brief firefight.

A tow-truck driver and a bystander were expected to recover from their wounds suffered in Tuesday's incident near the city's historical district.

Two cars confiscated by the FBI were being taken to the agency's headquarters here when the shots rang out, FBI spokeswoman Linda Vizi said.

Two tow trucks and a car filled with agents were nearing the lot when a minivan cut them off. A man leaped out of the van brandishing a gun and declared, "I'm taking those cars. They're mine," Vizi said.

The gunman traded shots with one of the tow-truck operators, who was armed with a handgun, before escaping in the minivan, police said.

No shots were believed to have been fired by FBI personnel, police said. The truck drivers were not agents. Authorities would not say who shot the female bystander in the foot.