Mandurah Detectives have released images of a man they believe can help with their investigation.
Police continue to appeal for information in relation to an incident in Greenfields on Thursday, July 26.
Around 10:45pm, a 23-year-old man was struck on the head by a man on a BMX bike, while walking along Waldron Boulevard in Greenfields.
The offender then threatened the victim with a knife before stealing his bag and riding east along Waldron Boulevard towards Murdoch Drive.
READ MORE: DETECTIVES PROBE GREENFIELDS ARMED ROBBERY
The offender is described as 18 to 20 years of age, with brown skin and a slim build, approximately 178cms tall and short dark hair.
He was wearing shorts and a hoodie.
The victim was treated in hospital for a head and shoulder injury received during the robbery.
Detectives would like to speak to anyone who was in the area around the time of the incident who may have seen a person on a BMX bike.
Anyone with any information is urged to call Crime Stoppers on 1800 333 000 or report online at www.crimestopperswa.com.au
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