The family of Jill Meagher have appealed for calm as a Facebook campaign against her murderer threatens their hopes of justice.

A major row is brewing in Australia as Adrian Ernest Bayley awaits trial for Meagher’s rape and murder in Melbourne.

Over 30,000 people marched in memory of Meagher on Sunday, on the very route she would have taken home from a night out with co-workers before her murder last week.

As they called for justice, police and the Meagher family have warned that social networking sites could threaten the case against Bailey under Australian law.

Her distraught husband Tom has warned of a mistrial if the growing hatred against Bayley on social network sites impinges on the trial.

And the family’s fears were magnified on Monday when Facebook refused to take down a page that is inciting hatred against Bayley.

Victoria state police have confirmed to Australian newspaper The Age that the contents of the site could damage their case.

Chief Commissioner Ken Lay told the paper that social media had been enormously helpful in the investigation into Meagher’s death but is now causing a concern.

He confirmed that police contacted Facebook over the weekend and asked the social media giant to remove a particular page.

There are several pages on Facebook related to the case but one in particular is calling for Bayley to be killed in prison.

Commission Lay said: “Now they’ve [Facebook] refused to do that, so we’re just working our way through that about what we can do now.

“But it is disappointing, and when you see the public, the hatred that’s incited by some of these sites, it is very much the antithesis of what we saw yesterday with 30,000 people taking to the streets saying let’s try and make this a safer and fairer community.”

Grieving husband Tom Meagher has warned that the negative comments could have an impact on the criminal case against Bayley.

He said: “I just wanted to say very briefly that despite the fact that this is the worst thing we’ll ever go through in our lives, I’ve been really humbled by the support from the Australian public, the fine efforts of police and all of the friends, family who’ve put their lives on hold to help us out.

“And while I appreciate all the support, I would just like to mention that negative comments on social media may hurt legal proceedings, so please be mindful of that.”

Facebook has yet to comment on the story to the Australian media.

Commissioner Lay also said that, despite the horrific nature of the Irish woman’s disappearance and death, Bayley is entitled to a fair trial.

He added: “We will go through the process and let the courts make the determination and deal with it as they see fit. That’s not for Facebook pages or anyone else to be taking justice into their own hands.”

The police warning came as Melbourne and Meagher’s hometown of Drogheda remembered the 29-year-old with a series of events over the weekend.

The Age reports that a 20-metre long mural has been painted on Hosier Lane in the city with the simple, yet poignant, message: Rest In Peace Jill.

Lord Mayor Robert Doyle told the paper the mural captured the mood of the city following Meagher’s death.

He said: “Whether it stays longer term is probably a question for the new council, but it is an appropriate reminder to us at the moment.

“My suggestion would be we leave it for at least a short period of time before we decide whether it stays there permanently or not.”

Victim Jill Meagher, photographed with her husband TomFamily's own