SINGAPORE - The families of the couple who abused their flatmate until she died have apologised to the victim's family while urging the public not to let their outrage spill over to them.

The eldest brother of Tan Hui Zhen told the media outside the courtroom after the couple was sentenced on Friday (Dec 1) that he wanted to say sorry to Ms Annie Ee Yu Lian's family, while acknowledging that an apology was not enough.

"We are fully agreeable that they should be punished for what they have done," said the man in his 30s, who wanted to be known only as Mr Tan. He said anyone would "feel disturbed" by what his sister and brother-in-law Pua Hak Chuan had done to Ms Ee.

The case has generated public outrage over the couple's horrific acts of abuse. An online petition seeking harsher punishment has gathered more than 20,000 signatures.

Mr Tan added that while members of the public are free to comment, he pleaded with them to "rest it as it is".

"Those who are responsible for the acts are going to be punished. There should not be any more unfortunate happenings to people related to them," he added.

He dispelled speculation that the couple were facing less severe charges as a result of their family background or money, noting that lawyer Josephus Tan from Invictus Law Corporation was acting for them on a pro bono basis.

He said his sister's mental condition had been "under-reported" in the media.

"We did observe signs of her being psychologically not that normal... It's most unfortunate that there wasn't any initiative to seek professional help prior to the tragedy happening."

He added that the family are still committed to supporting her: "Not because we condone what has been done... but that's our social responsibility."

Separately, Pua's mother said through lawyer Josephus Tan that she was deeply apologetic to the victim's family and that her son got what he deserved.

The woman in her 60s also asked for the public's understanding and forgiveness.

Mr Josephus Tan said families of both accused have been under "tremendous pressure" in the past few days, after details of the abuse were revealed in court when they pleaded guilty on Monday.