Investigators are reviewing surveillance video from a nearby business, according to sources close to the probe.
A gas station attendant on Admiral Wilson Boulevard said a Camden police detective had stopped by Sunday morning asking whether anyone in a white car or van had filled up gasoline containers.
The man, who asked not to be identified for fear of reprisal, said two men had filled a small container around 2 or 3 a.m. Sunday.
"There's been a lot of fires in a short period of time," the attendant said. "Something funny is going on."
The theory that all three are the handiwork of a serial arsonist follows a news conference last week in which Camden Mayor Dana L. Redd voiced concern over the short time frame in which the first two fires occurred.
Causes of those fires - June 9 at a former tire warehouse in the city's Gateway section and on June 11 at an abandoned garment factory in the Waterfront South district - have not yet been determined. The Reliable Tire Co. inferno destroyed 23 buildings and displaced more than 16 families.
Regarding Sunday's soap plant fire, a man was briefly taken into custody in the morning for questioning and later released, according to sources.
The blaze started around 5:15 a.m. Sunday with flames scaling a 60-foot-high structure on the property, residents said.
The U.S. Environmental Protection Agency had completed a six-month, $1 million cleanup at the site in March, removing asbestos and more than 400 containers of hazardous, flammable chemicals.
Referring to what had until recently been on the site, Robert Corrales, a spokesman for the Mayor's Office, said of Sunday's fire: "It could have been really bad."
The factory has been abandoned for at least a couple years, residents said.
