Police are searching for a man who indecently assaulted a 30-year-old woman on a crowded Perth-bound train earlier this month.
The woman boarded the Fremantle line train at Subiaco station just after 6pm on April 8.
A police spokeswoman said she stood in the last carriage and held onto a pole next to the doors because the train was "fairly full".
"During the journey, a man standing next to her indecently assaulted her," she said.
"There were numerous people on the train during the incident."
The man is described as aged in his mid-20s and about 165cm tall with an olive complexion, slim build and short black hair.
He wore a grey shirt with a black motif on the front.
Police have released CCTV footage of a man they believe can help with the investigation.
Officers would like to speak to anyone who saw the man at the time of the incident or noticed him before the train arrived at Subiaco station.
Anyone with information is asked to call Crime Stoppers on 1800 333 000.