Warning: This story contains details and content that some readers may find distressing.

The man responsible for what his defence lawyer described as one of the most depraved and monstrous murders Western Australia has ever seen has been sentenced to life behind bars.

Alexander Mark Sutton kept a journal detailing his plan to torture and kill Perth father Patrik Weiss.

For months, the then-19-year-old had been messaging former West Coast Eagles masseuse Patrik Weiss on a sex fetish website.

The father eventually agreed for the younger man to come to his Lockridge home, in the city's north-east, two years ago.

Weiss had bound, gagged and blindfolded himself on his bed waiting for Sutton to arrive.

Once inside, the teenager hit the 45-year-old twice to the head with an axe, fracturing his skull.

Police later found depraved journal entries at Sutton's home.

He wrote, "I am going to kill him to see the blood".

"He will be a guinea pig. Maybe I will eat part of him to see if I like it," another entry read.

He also posted on Instagram.

"I'm going to kill someone in three weeks… he's putting himself in such a vulnerable position," he posted, in all capitals.

"It's like Christmas morning and a present has been put in front of me."

His lawyer described the crime as "the stuff of horror movies" and "as close to an example of evil as one can imagine".

She said Sutton had spent months planning and entrapping Weiss "with the intention of performing the most perverted acts".

Weiss' former partner was in tears as she read victim impact statements written by their children.  

His daughter said she didn't understand how someone could do something so awful. 

His son said what happened hurt their whole family and changed their lives forever.

Sutton was sentenced to life behind bars with a minimum of 20 years.

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