Two women responsible for a violent assault on a young girl in a bath, recorded and broadcast on BlackBerry Messenger, have already been prosecuted, police said.
Shocking footage of the "horrendous, prolonged attack" prompted an urgent appeal for information.
Dressed in pyjamas the victim is repeatedly punched and beaten and bathroom detergents poured over her.
Officers feared for the welfare of the victim who was beaten unconscious in the distressing video sequence.
Anxious parents triggered the alert by calling South Wales Police to report that the footage was being distributed in the Cardiff area.
Several passed on information claiming to know the identity of the attackers and suggesting where they were from south Wales.
Police arrested and questioned a 16-year-old girl as part of their investigation, before releasing her without charge.
But the two female attackers were actually from Liverpool and were prosecuted and convicted of assault last month, police said on Thursday.
The shocking video footage of the attack dates back a considerable time before that and South Wales Police is no longer investigating the assault.
"It has been confirmed that the incident took place in Liverpool and the people responsible have been dealt with by court," a spokeswoman said.
"The press and public are thanked for their assistance."