The heist began with a thief backing a large, white box truck up behind a Virginia mall around 3:30 a.m. one day in early April, according to a search warrant. The man wasn't looking for cash or electronics, but something stranger: used cooking grease.

He siphoned about 150 gallons of the stinking, viscous liquid from a dumpster behind a Burger King, before a police officer patrolling Annandale Shopping Center busted him, according to the search warrant, filed in Fairfax County.

The crime is not new, but law enforcement officials say thieves are targeting the stuff used to make french fries and fried chicken anew because of a run-up in biodiesel prices in the past couple of years. Cooking grease can be turned into the fuel, creating a surprisingly lucrative black market for a substance most people wouldn't touch.

The National Renderers Association estimates that up to $75 million worth of old cooking grease is stolen each year.

"I've been a detective for three years," said Jeremy LeVan, who worked the Fairfax County case. "It's at the top of the oddest things I've seen stolen so far."

Restaurants typically contract with a rendering company to haul off cooking grease. The company pays the restaurant a fee and then recycles and sells the grease for components for such things as biofuel, animal feed or fats used in perfume.

Charles Gittins, a corporate lawyer and law enforcement liaison for Valley Proteins of Winchester, Virginia, said his company lost $5 million in grease thefts and an additional $1 million in damage to locking grease dumpsters in 2015, the last year they calculated totals. His company was also the victim in the recent Fairfax County case.

"You can make $10,000 in a night," Gittins said of grease theft. "You buy a junker truck. You buy a 275-gallon container at a tractor supply store. You get a pump and you're in business. You can run five nights a week."

Alvaro Mendez Flores of Richmond, Virginia, is facing grand larceny and other charges in connection with the grease theft at the Annandale Shopping Center on April 4, police said. When police searched his truck, they found a 1,600-gallon tank, water pumps and hoses used to pump the grease, according to the search warrant.

Mendez Flores told police he owned two box trucks and was part of a group that travels around northern Virginia and Maryland stealing grease, according to the search warrant, which describes Mendez Flores's statements to detectives. Gittins and LeVan said the Washington area is a hotbed of grease theft because the concentration of restaurants is high.

After taking the grease, Mendez Flores told detectives, he returned to Richmond and turned the truck over to his boss.

Mendez Flores's boss took the grease somewhere to dispose of it, but Mendez Flores told detectives he did not know where. Mendez Flores was paid about 25 cents per gallon of grease, netting him between $300 and $400 per trip to northern Virginia.

Mendez Flores also told detectives he had stolen between 800 and 900 gallons of grease the previous week from about seven businesses in northern Virginia, according to the search warrant.

A phone number could not be located for Mendez Flores, and his attorney did not respond to a request for comment. Detectives filed the search warrant to examine the contents of Mendez Flores's phone.

Gittins said Mendez Flores's group has been on his radar for at least a couple of years, but it was difficult to catch them in the act. LeVan said grease thieves typically work in the early morning hours and sometimes wear protective coveralls or construction vests to create the impression they are on legitimate business.

LeVan said six grease thefts have been reported in Fairfax County over the past year, but he suspects many more go unreported. LeVan said he is exploring whether Mendez Flores may be tied to any of the other cases.

"It's like people stealing copper and taking it to recycling to get money," LeVan said.