1. Various wide shots of warehouse containing drug tunnel
2. Close of armed Federal Agents
3. Mid of entrance to area of warehouse where drug tunnel was found
4. Immigration and Customs Enforcement (ICE) agent climbing down into tunnel entrance
5. Agent pointing out hydraulic buttons that open door of tunnel
6. Various of tools and shovels used to dig tunnel
7. Mid of monitor showing night vision image of tunnel below, panning to ICE agent preparing to climbing down hole
8. Mid of tunnel, following ICE agent
9. ICE agent Bob (no last name given), showing stairs built in tunnel
10. SOUNDBITE (English) Immigration and Customs Enforcement agent:
"This is the stair system, it's about a 70 foot drop. And you can see where they cut the stairs out, obviously coming up. And this is how they get from the level of the tunnel and the rail up into the level just underneath ground level."
11. Tracking shot following ICE agent climbing up stairs in tunnel
12. Various of tunnel
13. Various of rail track and electrical cables in tunnel
14. Various of entrance to tunnel
15. SOUNDBITE (English): Tim Durst, Immigration and Customs Enforcement agent:
"To an extent this is somewhat of a cat and mouse game. As long as there's demand for the supply of drugs in the United States then the drug smuggling organisations will continue to find a way to smuggle drugs into the United States."
16. Mid of monitor showing night vision image in tunnel
17. Mid of night vision camera in tunnel
18. Tracking shot of ICE agent climbing back toward entrance
19. SOUNDBITE (English) Tim Durst, Immigration and Customs Enforcement agent:
"They're looking to find new ways to move drugs and we're looking to find the ways that they're moving drugs. Their hope is they get a tunnel completed, they can move a lot of drugs into the United States and get a good return on their investment. Our hope is we find tunnels or the boats or whatever next they're next going to before they get a return on their investment."
20. Tunnel Task Force members from ICE, DEA and Border Patrol entering border warehouse
21. Tracking shot of agents walking through business
22. Mid of ICE agent "Ryan" interviewing business owner, Ron Soto
23. SOUNDBITE (English) Ron Soto, Warehouse Business Owner:
"The last tunnel that was found was next to one of my associates and he was shocked. There was nothing that he could have noticed before or made him think there was something going on."
24. Wide of border fence by warehouse complex, panning back to wide of warehouses
US federal authorities were on Thursday knocking on doors and asking for help from warehouse owners and tenants close to the border with Mexico after two major underground passages were discovered last month.
The cross-border tunnels - housed in warehouses in San Diego's Otay Mesa industrial area - were used to smuggle huge amounts of drugs from Tijuana, Mexico, according to the authorities.
Agents hope to learn more about the 12-thousand businesses that occupy Otay Mesa's non-descript warehouses and low-slung office parks near one of nation's busiest border crossings for cargo.
The streets hum with cargo trucks by day and fall silent on nights and weekends.
An Immigration and Customs Enforcement agent who visited two offices on Thursday peppered managers with questions before asking to look around: What line of work are you in? Who is your landlord? How many neighbouring suites are leased?
The tunnels discovered last month ran about 2,000 feet (600 metres) and were equipped with rail car, lighting and ventilation systems.
According to US authorities, both were the work of Mexico's Sinaloa cartel, headed by that country's most-wanted drug lord, Joaquin "El Chapo" Guzman.
The discoveries produced some of the largest marijuana seizures in the United States.
A passage discovered on 2 November (2010) which ran between warehouses in Tijuana and San Diego resulted in seizures of 30 tonnes 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 more than 20 tonnes on both sides of the border.
Outlets for the tunnel found last week were in bustling office parks, only 800 feet (245 metres) a part.