A disturbing discovery near an abandoned plant off I-19.

A documentary crew is shown an underground bunker believed to be used for human trafficking of children.

Tucson Police tells us that they are not ruling out the possibility that it was used for human trafficking, but they say they believe the bunker is most likely being used as a homeless camp.

Former Navy Seal Craig Sawyer is currently filming "Contraland" to expose the dark side of child sex slavery.

Sawyer tells KGUN 9 a homeless advocacy group called his crew after they discovered the underground bunker -- shielded from plain sight -- at an abandoned cement plant -- shielded from plain sight.

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They found wrist restraints on a tree, swings, children's clothing and furniture inside and outside the cramped bunker.

The group reported the find to law enforcement.

Stay with KGUN9-TV and kgun9.com for more information on this developing story.