Officers are investigating two indecent exposures and a sexual assault in south Manchester.
At 4.30am on Friday 9 September 2011, a 39-year-old woman was sitting in a bus shelter waiting for a bus on Palatine Road, West Didsbury.
A man drove past, parked his car up, went into the bus shelter and stood as if he were reading the timetable.
The woman looked up to see if her bus was coming and noticed that the man was exposing himself.
She stood up and walked away and the man went back to his car.
Between 1.10am and 1.25am on Friday 16 September 2011, two women, aged 21 and 22, were walking along Parsonage Road, Withington.
They got to the junction of Fairholme Road and noticed that a man was standing on the pavement, performing a sexual act.
The women walked past and, when they turned around to see where he was, the man was walking off away from them.
Between 2.45am and 3am on Friday 16 September 2011, a 20-year-old woman was walking along Heaton Road, Withington, after taking a taxi from Manchester.
She heard footsteps behind her so stood aside to let the person pass. She was pushed up against a fence and a man lifted the skirt and sexually assaulted her.
A car drove past and the man ran off along Heaton Road and turned onto Burlington Road.
In all three incidents, the offender was described as being a white man in his 20s or 30s with short dark hair and of chubby build.
Detective Inspector Mark Radford, based at South Manchester CID, said: "These incidents are very worrying and we are looking at the possibility that the same man is responsible for all three.
"We are determined to catch him because people from our community should be able to go out free from their journey or night out being blighted by someone like this - and we ask the community to support our efforts: if you have seen or know something about these incidents, please contact us.
"We are particularly keen to speak to the driver of the car who disturbed the man sexually assaulting a woman.
"Extra high-visibility officers will be patrolling the streets in the evenings this weekend and anyone with concerns is welcome to speak to them for advice and support.
"We are also reminding people of some tips that can help them stay safe at night: plan your journey out and back and try to use prearranged transport, if you must walk please do so in a group where possible and keep to busy, well-lit areas."
Anyone with information is asked to call officers at South Manchester CID on 0161 856 6152 or the independent charity Crimestoppers, anonymously, on 0800 555 111.