The girl wept and her family condemned the decision as ''a joke'' after Chief Justice Terence Higgins ordered the jury to find the married public servant not guilty.

''What a load of shit,'' the girl's father said.

The chief justice found that the charge against the man, who can only be identified as PM, of using a carriage service to transmit offensive material, could not be made out after the girl gave evidence that she was not offended by the emails at the time they were exchanged in April and May 2006.

The judge suggested that the Government consider new laws, to make it a specific offence to exchange lewd messages with a child, before he directed the jury to record a not guilty verdict.

''Whether it ought to be an offence to communicate in those terms with a person under the age of 16 years is a matter the legislature might want to look at,'' the chief justice told the court.

Police had initially charged PM with procuring a minor for sex.

After evidence at a committal hearing made it clear that the girl's flirtatious behaviour towards the man meant the charge could not be supported, Commonwealth prosecutors persisted with the offensive material charges.

The married public servant admitted to sending a series of emails to the alleged victim, who went to school with his child. In one message, the man allegedly addressed the girl with, ''Hey sexy!'' and in another he wrote, ''We may even have to do some study together.''

The jury of eight men and four women were each given a 120-page record of emails sent between the defendant and the young person.

Chief Justice Higgins said yesterday the child had initiated the email exchanges acting on a ''crush'' she had developed on the older man.

''There was no doubt that the child initiated the conversations, set the tone for the conversations and was not offended by them,'' the judge said.

''The question is not whether the conduct was reprehensible, it is whether it was offensive.''

For more on this story, see today's Canberra Times.