Mr ONeill, 60, who oversees safety on Victorian public transport, suffered three fractured ribs and bleeding on the brain.
Despite recent changes to prison regulations that prevent inmates from using social media via third parties, hundreds of comments have been posted on Mr Stephens' Facebook page since he was remanded on June 19.
A person purporting to be Mr Stephens in another Facebook exchange claims to be the victim of mob justice.
"I have been the bigger person from day one. It's all of you that wanted kangaroo court, mob justice, screaming for my families [sic] blood. Every one should let the courts handle it," the post says.
A number of posts on Mr Stephens' Facebook account appear to abuse or threaten "trolls" who make comments on the site.
One person is told by a person purporting to be Mr Stephens: "[I will] sqeeuze [sic] you like a pimple".
Another man is challenged to a fight, while others are called "fag" and "retard".
On Sunday, a spokeswoman for the Department of Justice and Community Safety said all prisoners were denied access to the internet and social media.
"It is a prison offence to commission other individuals to post something on social media on behalf of a prisoner," she said.
"The Department of Justice and Community Safety will thoroughly investigate this social media activity. Any prisoner found to be contravening prison regulations faces disciplinary action."
Last month, the father of Jay and Isaiah Stephens was charged after allegedly threatening police on social media.
Jared Pihlgren, 49, became the first person to be charged under new laws introduced earlier this year making it an offence to intimidate a law enforcement officer or member of their family.
The offence carries a maximum penalty of 10 years jail.
One of the social media posts, which has since been deleted, allegedly read: Id p--s on you Chris ONeill ya maggot dog. I got zero respect and you know why. F--- the police and your crew ya swine. You attack mine, god help yours".
Mr Pihlgren was granted bail on July 5 on the condition that he not use social media or contact his sons.
Senior Crime Reporter