A man has been arrested on suspicion of rape after two women got into taxis and were attacked.
Police believe the incidents, on January 20 and on Saturday in Newbury, are linked.
In both incidents the victims, in their 20s, described being picked up by a taxi, or a car purporting to be one, which was driven by an Asian man, Thames Valley Police said.
A 40-year-old man from the town was detained on Monday on suspicion of the second rape and later also arrested over the earlier offence.
On Thursday the force said he had been released under investigation as it appealed for witnesses or anyone with information to come forward.
A woman in her 20s left the Vault nightclub in Newbury with a friend and waited by a bus stop in Market Street.
At around 1.30am on January 20 she was picked up by a vehicle believed to be a taxi in nearby Mayors Lane.
She stopped at a cash point and returned to the taxi and was raped in an unknown location by the driver who was described as an Asian man, police said.
On Saturday, a 29-year-old woman left the Coopers Arms in Bartholomew Street and got into a taxi near the Inches Yard roundabout at around 4.20am.
She was driven to a property in an unknown location where she was raped.
The driver was described as an Asian man who was around 5ft 8ins tall, aged in his 30s and slim with a strong Asian accent.
It is not yet clear whether the driver carried out the attack or if there was another offender who attacked her inside the property, a force spokesman said.
Detective Chief Inspector Matt Stone said: “I am making an appeal to anyone with information about either of these serious offences to contact the police immediately.
“Detectives investigating both incidents now believe the two offences to be linked.
“I want to assure the public that everything is being done to locate and bring the offender or offenders to justice.
“This is a complex investigation involving obtaining and reviewing hundreds of hours of CCTV, carrying out painstaking forensic work as well as taking statements from potential witnesses.
“It is possible the offender or offenders have confided in someone about what they have done so if you have any information please do the right thing and come forward.”
The force reminded victims their identity would be protected by law and they would receive support from trained officers.
Deputy local policing area commander Lindsey Finch said the force would step up officer patrols in the town over the next few days and urged people only to use licensed taxis, book in advance and avoid travelling alone if possible.
Anyone with information can call police on 101 quoting 782 (1/3) or Crimestoppers anonymously on 0800 555 111.