Fawkner Embona Taskforce detectives have released CCTV images following an armed robbery at a convenience store in Sunbury last weekend.
Investigators have been told a man entered the Gap Road store about 2.45am on Sunday 2 June wearing a black motorcycle helmet.
The man, armed with a knife, made demands for cash.
He then fled on foot with some cash and was last seen heading east on Gap Road.
No one was injured during the incident.
The offender is described as being Caucasian, aged in his 40s, solid build and approximately 185cm tall.
He was wearing a Suzuki motorcycle jacket, jeans and runners.
Police believe the black motorcycle helmet had stickers on the side of it.