The seedy industrial area in San Diego's Otay Mesa area will go unnoticed no more.
That's the message federal officials are sending drug smugglers by flooding the zone with agents, who are knocking on doors and asking questions.
The area is getting paying extra attention after two major drug smuggling tunnels -- linking San Diego to Tijuana -- were discovered last month.
They hope to learn more about the 12,000 businesses that occupy Otay Mesa's nondescript warehouses and low-slung office parks. It's an area where people who pay rent in cash come and go at odd hours, walls vibrate from jackhammers and the streets hum with cargo trucks by day and fall silent on nights and weekends.
Now the feds are asking store owners to help them out.
"We're trying to get as many eyes and ears in the community as we can," Jonathon White, the Drug Enforcement Administration's San Ysidro agent in charge, reassured one manager, a customs broker.
An Immigration and Customs Enforcement agent who visited two offices Thursday peppered managers with questions before asking to look around: What line of work are you in? Who is your landlord? How many neighboring suites are leased?
The tunnels discovered last month ran about 2,000 feet and were equipped with rail car, lighting and ventilation systems. According to U.S. authorities, both were the work of México's Sinaloa cartel, headed by that country's most-wanted drug lord, Joaquín "El Chapo" Guzman.
The discoveries produced some of the largest marijuana seizures in the United States. A 600-yard-long passage discovered Nov. 2 that ran between warehouses in Tijuana and San Diego resulted in seizures of 30 tons on both sides of the border.
A tunnel found on Thanksgiving Day, which ran from a Tijuana home to two San Diego warehouses, produced seizures of than 20 tons on both sides of the border.
Outlets for the tunnel found last week were in bustling office parks, only 800 feet part.
Looking back, neighbors said they missed clear warning signs. One next-door neighbor remembers hearing voices through the walls at night and rarely seeing anyone during the day. The front door was spray-painted to prevent anyone from looking inside.
Mario Rodríguez, who worked next door to the tunnel's other outlet, said he never saw anyone come or go.
"We don't realize until it's too late," said Rodríguez, 46. "Look over there, across the street. I have no idea what they do."
Based on reporting by the Associated Press.