MANDURAH Detectives are investigating allegations a girl was indecently assaulted on a bus travelling from Mandurah to Falcon.
Sergeant Vance Davison said the incident was on October 3 and the girl was between 13 and `16 years old.
At about 4.35pm a man sat next to the girl and began a conversation.
Police said a short time later, it is alleged the man indecently assaulted her before she screamed.
With the assistance of two passengers, the girl was able to get away from the man.
The man is described as fair skinned, between 30 to 40 years of age, medium build, with dark coloured beard and a moustache.
He was wearing a baseball cap backwards, a dark long sleeved jumper and light long pants.
Police have released CCTV images of a man they believe may be able to assist them with their investigation.
Anyone with information should call Crime Stoppers on 1800 333 000 or report the information online at www.crimestopperswa.com.au.