Since the premiere of the CBS TV series "Zoo" on June 30, we've witnessed a growing number of violent animal attacks worldwide.

American zoologist Jackson Oz (James Wolk) noticed the animals' strange behavior during safaris he hosted in Africa. He has teamed up with researchers to discover why animals are attacking people, but so far, little progress has been made.

In "Zoo" Episode 3, "The Silence of the Cicadas," Jackson and Abraham Kenyatta (Nonso Anozie) traveled to Japan to find Professor Robert Oz's (Ken Olin) research involving animals.

Jamie Campbell (Kristen Connelly) and Mitch Morgan (Billy Burke) traveled to Jamie's hometown in Louisiana to show a senator their findings of abnormal zoo lion behavior. They also presented Jamie's case against Reiden Global.

Since episode one, Jamie has pursued the theory that chemicals produced by the company have caused lions to communicate with each other and attack humans.

Fans also learned that Jamie's vendetta against the chemical giant stems from something much more personal. When Jamie was 11 her mom was diagnosed with cancer. Eventually, there were 26 more people in their neighborhood diagnosed with cancer. She explained that as "sick farmers in a tidewater town" their community tried to sue the corporate chemical giant but lost.

Meanwhile, Mississippi death row inmate Evan Lee Hartley (Marcus Hester), whose execution date was fast approaching, often stared through the fence at a lone wolf sitting in the prison yard. There seemed to be a mysterious connection between the two.

And then it happened -- a wolf pack stormed the prison and attacked prison guards and staff. In the commotion, a kitchen fire triggered an alarm system that opened all the cell doors.

The death row inmate escaped. The former inmate gave the pack leader a nod of thanks before disappearing toward an unknown destination.

It wasn't a random animal attack -- it was a prison break.

In "Zoo" Episode 4 "Pack Mentality," Jackson, Abraham, Mitch, Jamie and Chloe Tousignant (Nora Arnezeder) help FBI Agent Ben Shafer (Geoff Stults) investigate the wolf attack on the Mississippi prison. Mitch and Abraham leave the team to catch one of the wolves. Chloe, Jackson and Jamie discover that Evan Lee Hartley might somehow be involved in orchestrating the attack.

"Zoo" is a drama television series based on the novel of the same title written by James Patterson and Michael Ledwidge.

Watch "Zoo" Episode 4 "Pack Mentality" on Tuesday, July 21 at 9 p.m. ET on CBS.

What role do you think death row inmate Evan Lee Hartley plays in the behavior of the wolves? Do you think the animals' behavior is caused by a chemical? Share your thoughts and theories in the comment section below.