Concerns are being raised about the effect social media is having on criminal prosecutions, with one judge warning the general public are tainting evidence.
Cases like the killing of Jill Meagher in Melbourne have highlighted the problem of trial by social media, and a South Australian judge says websites like Facebook are prejudicing witness accounts.
In an appeal judgment, Justice David Peek says "Facebook has spawned a new generation of private investigators".
He says it is now much easier for witnesses to discuss what they saw.
"The process itself has very great problems in relation to potential contamination of evidence," he said.
"Such problems are likely to occur when a victim of crime, or a witness to it, searches Facebook looking for the offender.
"In the age of Facebook, the spectre of what is little more than speculation upon speculation very quickly solidifying into an accepted view is something that must be very closely guarded against when trying to bridge the chasm between social chit-chat and proof beyond reasonable doubt in a court of law."
The appeal judgment overturned a man's conviction for assault.
The victim and a prosecution witness had used Facebook to find him.
Australian Lawyers Alliance president Tony Kerin says contamination of witness testimony is nothing new, but social media is providing a new medium through which it can occur.
He says it is likely to be a problem taking place around the globe.
"I imagine it's a matter that's probably affecting jurisdictions all around the world in the Western countries and probably others as well. In terms of our common law system of justice, it is an issue," he said.
'A new dimension'
In the assault case, police relied on witnesses' Facebook identifications instead of doing their own identification procedures.
The judge labelled that a very serious failure of the investigation and police now acknowledge they could have done better.
"It's inevitable given the prevalence of social media among people, particularly young people today," he said.
"It adds a new dimension to the criminal justice system, to the integrity of trials, and it's clearly challenging police, lawyers and judges in how to deal with it."
Professor Goldsmith has been investigating how police actions online can also compromise cases too.
"Police officers who, say, drink too much at a party [and] post some compromising picture of themselves inebriated on Facebook might find themselves in the witness box down the line facing a defence lawyer who's managed to find their picture or find their record on Facebook and then use that to bring their character into doubt," he said.
"That's a problem which is just emerging, which the police forces is going to have to reckon with because it affects the integrity of the trial.
"In that sense it affects the likelihood that people who have committed crimes will be in fact convicted."
And it is not just criminal cases. Social media is now being used to cast doubt on those involved in civil cases too.