District Court Judge David Dufton has been the target of online abuse after he convicted seven policemen of assault on democracy activist Ken Tsang.

Some critics have been posting disparaging messages on social media, calling Dufton a “dog judge” and threatening to surround his house and harm him, Apple Daily reports.

They accused Dufton of “political persecution” and bias in handling the case.

A spokesman for the Department of Justice said the DOJ is deeply concerned and will investigate.

He warned that any such attacks on a judge could constitute contempt of court. The DOJ will not hesitate to call in the police, he said.

Hong Kong Film director Clifton Ko posted several times on social media after Tuesday’s court ruling, saying the judge was biased and accusing him of “assisting the Hong Kong independence movement”.

Ko wrote on Facebook that “a fair verdict has a fair judge, a bad verdict means a dog judge”.

On Thursday, Ko said the judiciary had “clarified” the issue and that he will no longer comment on the matter.

Chan Kin-po of the Pro-China Politihk Social Strategic Facebook urged supporters to start a protest by surrounding Dufton’s house.

Progressive Lawyers Group founder Yam Kin-fung said the judiciary deemed that events are serious enough to be investigated.

But whether or not the commenters will be prosecuted is entirely up to the DOJ, he said.

Last year, Legislator Junius Kwan-yiu Ho opened himself up to contempt of court after posting an online selfie he took inside a court room. He was not prosecuted.

Yam said the commenters in the case of the seven policemen are liable to contempt of court charges if they have openly humiliated the judge.

On Friday, Dufton jailed the seven officers for two years.

Article originally appeared in EJ Insight on 17 February 2016