West Australian police have launched a murder investigation after the victim of a stabbing in Perth's south died in hospital.

Ian Michael Baz Bosch, 43, was stabbed in the neck at a bus stop on Cordelia Avenue in Coolbellup about 7:30am on Saturday.

He staggered to the nearby Coolbellup Shopping Centre for help and was taken to Fiona Stanley Hospital but died two days later.

Police were unable to speak to Mr Bosch before he died.

Officers have released closed circuit television footage of the moments before the stabbing.

The vision shows Mr Bosch arriving at the bus stop, appearing to check the timetable and sitting down with a green backpack before another male arrives about 15 seconds later.

Detective Senior Sergeant Tom Mills said police want to speak to the second man in the footage.

"He has dark hair, was wearing a dark, long-sleeve jacket and [what] appears to be a white T-shirt. He also had long dark trousers on and we believe he was wearing runners," he said.

"The mal, leaves the area of the bus stop, runs down Cordelia Avenue and turns left, and heads south along Coolbellup Avenue."

Police said in the hour leading up to the stabbing, Mr Bosch had caught a bus to the shopping centre from his Coolbellup home, but there were about seven to eight minutes where he was unaccounted for before he arrived at the bus stop and was stabbed.

The victim was a landscaper, had two children, and was estranged from his wife.

Detective Senior Sergeant Mills said Mr Bosch was 200 centimetres tall, and was hopeful someone in the area may recall seeing him that morning.

Police are still trying to establish if Mr Bosch and the man in the footage knew each other.

Officers have recovered the victim's backpack and do not believe he was robbed.

The weapon is yet to be found.