Williams said: “We took the reports from women who came forward, as well as the public feeling towards this behaviour, really seriously.”
She said throughout their investigation , officers had explored all lines of enquiry thoroughly, including digital forensic examination of various devices.
“The investigation was also reviewed by an experienced, senior detective to ensure no stone was left unturned,” she added.
“Predatory behaviour is completely unacceptable, and tackling this has been a priority for our night-time economy policing operation.”
The safety of people on nights out in the city remained their priority, the force said.
Under GMP’s Operation Safer Streets campaign, officers have made about 1,000 interventions with suspicious individuals and the same number of contacts with vulnerable people.
It had resulted in “significant reductions in offences such as rape”, the GMP spokesperson said.