Police are investigating a robbery in Morley earlier this month.
Mirrabooka Detectives allege that around 11pm on Friday March 8, the 24-year-old male victim was waking on Walter Road East while talking on his mobile phone.
He then sat down at a bus stop while continuing his call.
Two men have approached the victim.
The first man assaulted the victim and threatened him with a knife while demanding his wallet, while the second man took his phone.
An unknown man stopped his car and tried to assist the victim before he was also threatened with a knife.
The unknown man left in his car in an easterly direction.
The victim then ran across the road to a fast food outlet to call police.
The two men were last seen running east on Walter Road, and the phone was later located on Anzac Terrace in Bassendean.
The first man is described as 183 centimetres tall with a lean build, dark hair, and a tattoo on the front of his neck.
He was wearing dark trousers, a long sleeve white top and black shoes.
The second man is described as light skinned, 183 centimetres tall with a muscular build, 18-22 years old with a slight beard.
He was wearing dark clothing.
Detectives wish to speak to the unknown man who stopped to help.
Anyone with information should contact Crime Stoppers on 1800 333 000 or make an online report.
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