The police have so far linked two sexual assaults, but they are expected to appeal to other victims to come forward at a press conference later today.
The two attacks - one in London, the other in Essex - happened six years apart but an inquiry, known as Operation Catchment, has established "significant similarities which indicate the same man is responsible", police said.
In the most recent assault in March, a 36-year-old woman on her way home from work was attacked and raped on waste ground near Bermondsey railway station in south-east London. The man raped her and stole a small amount of cash. The man, who had at first demanded money, attackead the woman at about 7.30pm
In the other assault, at Brentwood, Essex, in February 1992, a 25-year- old woman was grabbed as she walked to her car and was forced to drive to a dimly lit area where she was raped.
The woman's handbag was dropped during the assault, but it was never recovered.
At the time, that incident was linked to a number of sexual assaults, including the rape a month earlier of a 22-year-old who was attacked at a station near Stevenage, Hertfordshire.
Essex Police said yesterday that they had set up an investigation with British Transport Police to hunt the attacker.
There has been heightened concern about safety on and around the railways this year after an upsurge in sexual assaults. Two teenagers travelling between London and the South Coast were attacked in separate incidents in January.
In January a Czech student of 19 was dragged into a toilet cubicle and raped while travelling on the Hastings to Charing Cross train. Hours later a 15-year-old girl was raped after apparently being followed by a man as she left Hastings railway station. These two cases have not been linked.