Sunday's deadly smuggling incident isn't unheard of. In fact, Interstate 35 is one of several known human trafficking corridors exploited by smugglers in Texas.

Truck drivers are not always accomplices of this dangerous scheme.

It's places such as truck stops in Laredo that locals say undocumented immigrants and smugglers begin their journey into the rest of the country. Hiding in tight spaces, sometimes unknowingly to truck drivers.

Every time, before heading north, Diango Flores inspects his red tractor trailer.

He opened the hood, looked under the motor, behind the cabin and even inside small compartments on the sides of the trailer.

Flores is not looking for mechanical issues, he's looking for people.

Flores says someone could try to hide a child or a small person as he opened one of the compartments.

It's a necessary routine, he said. After all he uses the interstate 35 to transport goods from Mexico into the U.S. and sometimes all the way to Canada.

Flores has been a truck driver for 5 years. He said he's lucky no one has tried to use his truck to make it through the Border Patrol checkpoint about 30 miles north of the border. Or at least not to his knowledge.

He says he wouldn't like to lose his visa or his job, much less get arrested and be thrown in jail. That's why Flores tries not to spend too much time idling at the border.

"Laredo has thousands of tractor trailers that basically transport goods from the border to northern cities everyday, every hour, said Laredo Police investigator Joe Baeza.

“A lot of the immigrants do hitch a ride unsuspectingly to those truck drivers," he added.

Baeza said this is an ongoing trend. Just last week, Border Patrol agents discovered 33 undocumented immigrants inside this locked trailer, he said. Many times the drivers are involved in human trafficking and resort to deadly measures in order to move people undetected.

It's a problem authorities on the border have dealt with for some time.

Investigator Baeza said they work with federal law enforcement to catch trailers loaded with humans before it's too late. He said as long as there is money to be made and people living under the radar, human trafficking will continue to thrive.