SINGAPORE - She was barely able to breathe because her ribs were fractured and was unable to stay awake given her weakened state from daily beatings and open wounds, but Miss Annie Ee knew she was in for more punishment.

The weapon, a large roll of shrink wrap weighing 1kg that her abusers knew she feared, was placed next to the woman she called "jie jie" (meaning older sister in Mandarin).

Her "jie jie", Tan Hui Zhen and husband Pua Hak Chuan, whom she referred to as "jie fu" (meaning brother-in-law in Mandarin), had returned home that evening on April 12, 2015, to find Miss Ee, 26, lying in her own urine.

They accused her of urinating on the floor to get attention. While she lay slumped in a chair from exhaustion as she was being scolded, the couple decided to punish her for her "bad attitude".

It would be the last round of beating Miss Ee, who was intellectually disabled, would suffer before dying in her sleep hours later in the early morning of April 13, 2015.

She was repeatedly hit using the shrink wrap and fell to the floor, but even the sight of her on the ground inching towards her room did not stop more abuse from raining down. Pua continued to use the shrink wrap to hit her legs, abdomen and buttocks, which already had open wounds and blisters.

Pua then picked up a plastic dustbin, lifted it over his head and smashed it down on Miss Ee with such force the bin cracked.

Throughout the last beating, Miss Ee continued to protect her abusers by muffling her pain and suppressing her screams and shouts. Earlier that day she had tried to commit suicide by cutting her wrists, having felt "useless" when she could not carry out Tan's instructions.

Hours before she died, Miss Ee told the couple that she felt "pain was everywhere", but they measured her blood pressure and concluded that she was "normal".

Miss Ee first met Tan when they were teenagers and they rekindled their friendship in 2013.

Estranged from her family, Miss Ee moved into Tan and Pua's four-room Woodlands flat in late 2013 and was given housework to do.

Details about Miss Ee's family were not shared in court documents.

Over the eight months of abuse - from August 2014 until her death on April 13, 2015 - Miss Ee started showing up for her waitressing job with bruises on her body, arms, face and neck.

The beatings and their increased intensity over time, with some sessions lasting up to two hours, meant she had difficulty walking, standing and breathing. She also became incontinent.

The couple also made Miss Ee surrender her salary of $1,200, from which she was given a weekly allowance of $50. This was later cut to $30.

When The Straits Times visited Miss Ee's former workplaces, ex-colleagues declined to comment on her case and said they had been told by the police not to share any details.

However, court documents revealed that they had noticed Miss Ee would often hide her injuries by applying a thick layer of concealer, letting down her hair and donning a cap.

She would keep quiet when questioned, but on one occasion had told an assistant manager "my family, loh", when asked about her injuries.

An autopsy report later revealed the extent of abuse she suffered at the hands of the couple: 12 fractured ribs and seven fractured vertebrae, a ruptured stomach and a body crowded with blisters and bruises.

Some of the injuries were so serious the couple used sanitary pads to dry the wounds and bandage them.

The autopsy report also said Miss Ee died of acute fat embolism. She had been beaten so severely that fatty tissue below the skin had separated from the muscle and entered her bloodstream, interfering with blood getting oxygen in the lungs and leading to progressive cardiac and respiratory failure.

The couple were sentenced to lengthy prison terms on Friday.

Tan, 33, was sentenced to 16½ years' jail, while Pua, 38, was given 14 years' jail and 14 strokes of the cane.

They were initially charged with murder, but the counts were amended after police completed investigations and on the basis of forensic pathologist reports.

Justice Hoo Sheau Peng said on Friday that Tan and Pua had abused the trust of a vulnerable victim who treated them as her family. When Miss Ee suffered in silence, this emboldened the couple to escalate the violence inflicted on her, said the judge.

Tan suffered from depression and borderline personality disorder. The judge said she gave this little weight but took into account as a mitigating factor that the couple had come clean in revealing what they had done to the victim.

The couple had pleaded guilty on Monday to various charges for the extensive torture of Miss Ee.

A person said to be Miss Ee's younger sister, who did not want to be named, told Channel NewsAsia through WhatsApp that her sister's freedom "was sometimes compromised" as the family was concerned Ms Ee's simple nature could lead to her being "bullied or cheated".

Her sister added: "My sister felt that our family was being unfair to her (by) not giving her the freedom to make her own friends… She felt that she was old enough to look after herself."

Miss Ee was said to be the eldest among her brothers and sister. She later moved out to live with Tan and Pua.

The family tried to prevent Miss Ee from being in touch with Tan as they believed Tan "was trying to manipulate" her, but Miss Ee "didn't believe what we told her, because she felt that (Tan) was always (on her side)", her sister said.

On the public apologies by the families of Tan and Pua, Miss Ee's sibling said her family "will never be able to forgive what (they) did, especially Tan".

Neighbours The Straits Times spoke to on Thursday said the trio did not interact much with others, but the sound of mahjong games could often be heard coming from the third-floor unit at Woodlands Avenue 9.

"Back then, I don't remember any shouts or screaming. We were all surprised to find out that such severe abuse was happening right under our noses," said a neighbour on the same floor who only wanted to be known as Miss Lee, 35, a secretary.

As Miss Ee normally left the flat around 9am when other residents had already gone to work, neighbours did not see her often, said retiree Xu Wei Jian, 70.

Miss Ee would often walk past his unit while he did repair work in the corridor and they would greet each other. He had no idea she was intellectually disabled as she carried herself well and was able to make normal conversation.

Mr Xu had on at least two occasions asked her why she often had bruises around her eyes. "Once, she said she had been beaten by a colleague, so I told her to tell her manager or call the police. The other times she said she fell, but I did wonder how it was possible that she could fall so often," said Mr Xu in Mandarin.

He added that she must have been too scared to tell anyone, but if she had just said something about the abuse he would have done something.

When asked if he regretted not alerting anyone to Miss Ee's injuries, Mr Xu said: "There's no use regretting, she's gone now. I never expected that the injuries could come from the people she lived with."