Police have issued a CCTV image of a man they want to speak to
Two men arrested over attacks on schoolgirls in which they had animal semen thrown at them have been released without charge.
There have been four confirmed attacks in Greater Manchester and two others which police believe may be linked.
In each a man has followed young girls before they discover they have been smeared with the liquid.
Two men, aged 27 and 30, were arrested on suspicion of sexual assault, but have been released.
Police have released a CCTV image of a man they want to speak to.
Det Insp Lynne Vernon, of Greater Manchester Police, said: "Thanks to the public's response in coming forward, a lot of work has been done by our officers during the last six weeks.
"All names that were given to the investigation team have been looked at and in two separate cases we made arrests. We can now confirm that none of these is the person responsible for that crime and they have been eliminated from our inquiry.
"We remain determined to catch this man and would ask that the public take another look at this image."
The first victim, a 14-year-old girl, was followed by a man on Kennedy Drive in Unsworth, on 13 November.
He asked her the time and was standing uncomfortably close to her.
When she got home, she noticed a sticky liquid on her tights.
The substance was analysed by police and later identified as animal semen.
In the latest attack, on 25 January, a man approached two girls, aged 15 and 16, on Pinfold Lane, Whitefield, and asked them the time.
One of the girls then noticed liquid dripping from her skirt.
In each incident, the offender was described as being a white man, aged between 25 and 35 and was carrying a bag.