While investigators continue to find out what led to death of 10 undocumented immigrants in San Antonio, prosecutors with Harris County District Attorney's Office said Houston came very close to having the same thing happen just a few weeks ago after 12 undocumented immigrants were rescued from the back of a Penske moving truck.

Three people are still in custody at the Harris County Jail, charged with human smuggling.

The prosecutor over the case said 30 more minutes inside that hot moving truck, and the people may not have been so lucky.

The door was shut and locked from the outside.

“It’s a Penske rental truck. They're not air conditioned. There's no ventilation. It's meant for moving your apartment or your home. Not for holding people," said JoAnne Musick with the Harris County District Attorney's Office.

Eleven adults and one child were on the verge of danger.

“You can imagine sort of baking in that truck, all day, all night, as you travel across Texas," Musick said.

How they got across the border is still unclear, but the truck originated out of San Juan, Texas, and was then found several hours later in Houston.

That’s where Musick says they would split up.

“Place a couple in each car and then travel on from there," Musick said.

Three people were arrested, and found on one of those suspects, Musick said, was a list.

“The ledger lists names, quantities and amounts of money. When you look at that ledger, it adds up to the number of individuals who were in the back of that truck," Musick said.

They each paid $1,500 to $2,500 to be there, seeking an escape to a better life in the United States, but instead, they became victims.

“People who smuggle, people who traffic, they’re in the business of exploiting people," Musick said.

And to hit the brakes on trafficking, DPS Troopers are specially trained.

“A large number of the troopers just ask, 'Can we look in the back of your vehicle?' and that’s when we find them," said Sgt. Richard Standifer with Texas DPS.

It’s constantly on their radar.

“You start talking to the driver, and he exhibits extreme nervousness or profuse sweating those types of things, those are what we would refer to as criminal indicators," Standifer said.

Those three suspects arrested are due in court at the end of August, but until then, prosecutors say they will be working to secure an indictment for each of them by a grand jury.