Former NSW police detective Craig Semple knows the mental toll of a high-stakes job.

For 25 years, Semple focused on high-risk law enforcement, dealing with drug, gang and homicide investigations and investigating some of Australia's most notorious criminals. 

It came with a cost- as Semple suffered from post-traumatic stress disorder and depression after retiring from the force.

He detailed a raw account of his experience in his memoir 'The Cop Who Fell to Earth'.

"I got to learn my job by training, being thrown in the deep end of the pool and learning to swim that way. I learned a lot about self-reliance. If that homicide happened in the city, the homicide squad would have picked it up- out there, I was it."

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