Inside the unfinished tunnel, via ICE.

By Steve Neavling

ticklethewire.com

The discovery shocked federal agents: An unfinished tunnel that ran from San Louis, Ariz., to a Mexican neighborhood featured a ventilation system, electrical wiring, water lines, a rail system and extensive reinforcement.

“This appears to be the most sophisticated tunnel in U.S. history, and certainly the most sophisticated I’ve seen in my career,” Carl E. Landrum, acting chief patrol agent with the Border Patrol’s Yuma sector, said, The Associated Press reports.

Discovered by Homeland Security Investigations in late July, officials believe it was intended for smuggling.

The tunnel was 3 feet wide and 4 feet high.

Excavation work on the tunnel, via ICE.