A judge has criticised paedophile hunters after the trial of an alleged sex offender collapsed.
David Poole told Cardiff Crown Court he trapped Adnan Khalid, 27, who was charged with grooming a 14-year-old.
Mr Poole, 38, was accused of giving misleading evidence in the trial of Mr Khalid, of Porth, Rhondda Cynon Taff.
Judge Thomas Crowther QC entered a formal not guilty verdict and criticised the paedophile hunting group for the trial collapsing.
Mr Poole, from Hereford, founded the group H Division and set up a fake profile on dating website Plenty of Fish claiming to be a 14-year-old called Chloe.
He arranged to meet Mr Khalid in Cardiff after messaging him on Whatsapp and filmed the sting.
Mr Khalid denied the offence and told police he believed he was speaking to a woman aged over 18.
Mr Poole arrived four hours late to the trial and then said he had passed photo evidence to the police, before admitting this was not true.
Judge Crowther said his answer was "at best inaccurate and at worst a lie".
He discharged the jury, saying: "This case underlines why criminal investigations should be conducted carefully, meticulously and by those who are trained and qualified to do so.
"When you are talking about a conviction, especially a sexual offence conviction, a high degree of reliability is needed in the evidence.
"The prosecution have taken the view that you could not find that degree of reliability in Mr Poole's evidence."
During the trial, Mr Poole said this was one of the group's "first stings" and was "a learning curve".
Speaking after the court case, a NSPCC Wales spokesman said online abuse and grooming was "one of the biggest child protection challenges we face".
"While we have every sympathy for people concerned about suspected abusers, we believe that identifying offenders and investigating crimes is best left to the police," he said.
"When members of the public take the law into their own hands it can run the risk of driving offenders underground, jeopardise on-going police work and the legal process or result in innocent people being harassed - all of which may put more children at risk."