Quentin Somerville

So it's just after six at night here in Tijuana. I'm at the headquarters of the state police. The agents are getting ready to go out on patrol. They've got a fleet of pickup trucks and they're all heavily armed. They're wearing body armor and they're all putting balaclavas on at the moment. And that's to protect their identity because being a cop in this town is extremely dangerous.

So it's just after six at night here in Tijuana. I'm at the headquarters of the state police. The agents are getting ready to go out on patrol. They've got a fleet of pickup trucks and they're all heavily armed. They're wearing body armor and they're all putting balaclavas on at the moment. And that's to protect their identity because being a cop in this town is extremely dangerous.

Ready for the action. That's a report that's just come in of gunfire over the police radio. It's a Saturday night here, so they're expecting a lot of drunkenness, a lot of drugs. By far the biggest, most dangerous drug here is fentanyl. So they're looking for anyone who's dealing. So it's another drug stop and the police have got the man against the vehicle. He's emptied his pockets.

Ready for the action. That's a report that's just come in of gunfire over the police radio. It's a Saturday night here, so they're expecting a lot of drunkenness, a lot of drugs. By far the biggest, most dangerous drug here is fentanyl. So they're looking for anyone who's dealing. So it's another drug stop and the police have got the man against the vehicle. He's emptied his pockets.

Fentanyl use is a growing problem here in Mexico. Still, most of it goes across the border to the United States. The ground is shifting along the border. Mexico has deployed 10,000 troops. Some 29 cartel leaders held by Mexico have been handed over to American law enforcement. And for the first time, a number of cartels have been designated terrorist organisations by the US.

Fentanyl use is a growing problem here in Mexico. Still, most of it goes across the border to the United States. The ground is shifting along the border. Mexico has deployed 10,000 troops. Some 29 cartel leaders held by Mexico have been handed over to American law enforcement. And for the first time, a number of cartels have been designated terrorist organisations by the US.

What we're trying to find out is just how so much of this drug is still making it into America. And up here, you might find some answers. We're just approaching a safe house. Inside is one of the foot soldiers of the cartels and a drugs mule. And they're making the final preparations for a fentanyl shipment to the United States tonight.

What we're trying to find out is just how so much of this drug is still making it into America. And up here, you might find some answers. We're just approaching a safe house. Inside is one of the foot soldiers of the cartels and a drugs mule. And they're making the final preparations for a fentanyl shipment to the United States tonight.

I watch as they place tightly wrapped packets of pills of synthetic opioid, 5,000 in total, inside the fuel tank of the car. It will be driven across a legal border crossing, right under the noses of US Customs. the drugs gang asked us to alter their voices. Do you ever feel guilty about all the people that it's killing?

I watch as they place tightly wrapped packets of pills of synthetic opioid, 5,000 in total, inside the fuel tank of the car. It will be driven across a legal border crossing, right under the noses of US Customs. the drugs gang asked us to alter their voices. Do you ever feel guilty about all the people that it's killing?

The cartels know that American traffickers are less likely to be stopped, so they use US citizens mostly to make the drive across the border. Watching the proceedings, to one side, a dealer from L.A. Again, we have changed his voice. How many pills do you shift a week in L.A. ?

The cartels know that American traffickers are less likely to be stopped, so they use US citizens mostly to make the drive across the border. Watching the proceedings, to one side, a dealer from L.A. Again, we have changed his voice. How many pills do you shift a week in L.A. ?

Mr. Trump, he's determined to stop the drugs trade.

Mr. Trump, he's determined to stop the drugs trade.

The cartels claim to be unfazed by the latest US threat to destroy them, but the Trump administration says this time is different. But the cartels didn't create America's opioid crisis, one that's been killing as many as 100,000 people a year. Those numbers are now falling, but this crisis started with doctors and American pharmaceutical companies over-prescribing painkillers.

The cartels claim to be unfazed by the latest US threat to destroy them, but the Trump administration says this time is different. But the cartels didn't create America's opioid crisis, one that's been killing as many as 100,000 people a year. Those numbers are now falling, but this crisis started with doctors and American pharmaceutical companies over-prescribing painkillers.

Neighbourhoods like Philadelphia's Kensington have been left ravaged.

Neighbourhoods like Philadelphia's Kensington have been left ravaged.

Here, Rosalind Pichardo of Operation Save Our City starts her day by checking on the locals.

Here, Rosalind Pichardo of Operation Save Our City starts her day by checking on the locals.