With America's heroin crisis reaching epidemic levels, there is more of the killer drug on America's streets than ever before.
Authorities are making more seizures along the Mexican border, but supply continues to increase. A sea of vehicles enters San Diego every day from Mexico. Any one of them could be carrying drugs.
"Our job here is to find that needle in the haystack," said Sidney K. Aki, Port Director, U.S. Customs and Border Protection San Ysidro and Otay Mesa Ports of Entry.
The State Department estimates 92,000 pounds of heroin were produced in 2014 in Mexico, most of it headed for the United States.
Yet, according to the drug enforcement agency, only 11,000 pounds were seized across the country. Aki said smugglers get more sophisticated every day.
"We've seen narcotics in transmissions, we've seen rear quarter panels, front quarter panels, dash boards," said Aki.
During our visit, inspectors found 22 bags of cocaine and meth in a spare tire. At another crossing, nine pounds of heroin hidden in a motorcycle and a suitcase. Officers question each traveler but they do not search every vehicle.
Instead, they rely on instinct, density readers and X-ray machines to find drugs. In between the ports, just two fences separate Mexico and the U.S., where agents face a different challenge.
Agent James Nielsen said in the past 15 years, they've discovered 59 sophisticated smuggling tunnels from Tijuana.
"Some of these tunnels are about a million dollars to construct," Nielsen said. "There's a lot of money involved here. So the threats always exist."
More heroin is seized on the San Diego border than anywhere in the country. But with the heroin epidemic hitting new highs every year, there's a long way to go.
The National Drug Control policy estimates that heroin seizures along the southwest border increased 296 percent from 2008 to 2013.
Officials say that also suggests that there has been a substantial increase in the amount of heroin that's entering the United States illegally.