While San Antonio's police chief, William McManus, said Sunday morning's incident was a case of human trafficking that has left 10 people dead, an expert on the issue said people should be careful using that term.

Melissa Torres, a Ph.D. in the University of Texas' School of Social Work, said that there is more to human trafficking than transporting a group of people from one place to another. In fact, you don't have to move to be considered a trafficking victim.

Torress said trafficking involves harboring and transporting a person by force, while smuggling could be voluntary.

However, one can lead to the other.

"In trafficking situations, it's more common that smuggling has been a part of it. But again, the smuggling situation itself might not have been my force. It might lead to trafficking, but that doesn't mean it's the same thing,” said Torress.

Right now, investigators don't know where the passengers are from. Torres said, whether it turns out to be smuggling or trafficking, immigration and law enforcement will be working with survivors.