The small village in northwest China's Gansu province which saw a whole family poisoned. [Photo/CCTV]

A mysterious case of murder in a small village in northwest China's Gansu province, which saw a whole family poisoned, had grabbed the attention of authorities and the public alike.

Yang Gailan, a 28-year-old mother is thought of administrating poison to her four kids aged from three to six, including a pair of five-year-old twins, before taking her own life on August 26.

It is argued that the suspect is herself a victim of poverty, having succumbed to despair as the destitute family led a life of frugality and misery.

The grief-stricken husband, Li Keying, was found dead a few days after the incident. He had returned back to the village a day after the incident took place, and went missing on September 2. His lifeless body was found in nearby woods after a two-day search operation.

Poison was confirmed to be behind his demise, yet it is unknown whether it was a case of suicide.

The case further proved to be an enigma, with mystery shrouding the details of what happened on that unfortunate day.

One witness, a villager who is surnamed Shi, said she heard shouting and cries coming from the house.

When people rushed to the ramshackle house, they found all four kids injured. Three had died, but the oldest daughter, who had sustained a crack on her skull, and the mother were still heavily breathing. Both were sent to the hospital immediately, but it was too late.

"Their family is poor, but Yang was always nice and cheerful. I can't imagine why she did this to her own children," one villager said.

Yang's 52-year-old father Yang Mantang and her 70-year-old grandmother Yang Lanfang, who shared the same living space with the family of six, spoke with heartache about their loss.

"I witnessed my great grandkids dying and I tried to stop Gailan and ask why she had to do this. Gailan grabbed me and said she would take all her children with her, no one will be left behind," the traumatized lady said, adding she could not understand her granddaughter's act.

Investigators are contemplating poverty as a motive that guided Yang to kill her own blood.

The family was financially struggling, and unable to make ends meet. Yang worked the land, and Li was a worker in the city. Of the estimated 7,000 yuan (over $1,000) he earned per year, over 3,000 (over $450) were sent home for his family's subsistence. Livestock helped the need family earn a few pennies.

However, the family was deprived of government allowance in 2013, when it was evaluated that the average personal income stood at 4,000 yuan (about $600) annually, higher than the 2,300 yuan ($343) limit set by the government.

The State Council Leading Group Office of Poverty Alleviation and Development is now jointly working with local police and Gansu Provincial Department of Civil Affairs to conduct further investigation.

At the end of 2014, China had 70 million people living below the nation’s poverty line of 2,300 yuan in annual income. However, poverty elimination is one of the country’s major goals, and Beijing aims to end poverty by 2020, when China’s 13th Five-Year Plan comes to an end.