Grieving families seek answers to why killer blaze occurred. The flames may have been extinguished, but anger over the fatal blaze at a Shanghai high-rise is still raging in the hearts of the victims' families and friends.

A mourner prays on Wednesday for victims of Monday's high-rise apartment block blaze in Shanghai, at the entrance of the fire-gutted building.

For a city renowned for its urban achievements, the question on the lips of horrified residents and those who escaped the burning 28-story tower is: "How could this happen?"

Police have already taken eight people into custody, including four unlicensed welders who were working on the building when the fire started.

The detentions came after experts on the investigation team sent by the State Council blamed the disaster on illegal practices, such as multi-layered subcontracting, and lax government supervision.

However, none of the statements so far released have dispelled suspicion among the public that corruption also played a significant part.

Monday's blaze in Jing'an district started during renovation work to improve the building's energy efficiency.

At least 53 people were killed, with another 36 people still missing.

Sixteen of the 71 people hospitalized are in critical condition.

In charge of that renovation work was Jiayi Building Decoration Engineering, the company being targeted by much of the public outrage.

The firm took over the contract after its parent company, Jing'an Construction, successfully bid for the 30-million-yuan ($4.5 million) project.

According to the registered information, Jiayi is a State-owned company that was founded in June 1987 with an initial registered capital of 240,000 yuan. The address given for its headquarters is a three-story office block in a rundown area dominated by migrant workers that is slated for redevelopment.

With no company sign outside, it is not an easy place to find. Only a handful of employees were onsite on Thursday. All of them declined to answer any questions.

The management office, which is on the third floor, was completely empty. Judging by the silk banners and certificates issued by city authorities that hung on the walls, Jiayi was an award-winning unit in 1990s.

Everything else pinned to the walls of this sparse space was out of date, with some internal information not updated since 2001.

"(Jiayi) is getting ready to be relocated due to the area's redevelopment," said an employee of one of the small companies that share the office block.

Since police detained Huang Peixin, Jiayi's corporate representative, for questioning, all projects involving the firm have been suspended.

Questions remain over how Jiayi was initially selected for the district government-led energy efficiency improvement project, which included three buildings: the one that caught fire and two nearby residential towers.

Information available on the authority's website states Jiayi, which employs 50 people, won 36 renovation contracts in Jing'an between June 2007 and September this year. The total value was more than 28 million yuan.

These projects mainly involved schools and buildings used by government departments or State-owned enterprises.

However, fears over the company's qualifications were raised in 2006, when the Shanghai Urban Construction and Communication Commission reported that it "did not provide conditions for safe construction".

Jiayi also failed an annual safety quality test in 2008, according to information published on the commission's website.

Even last month, Shanghai Jing'an Construction Supervision, the firm hired to oversee the quality of the energy efficiency improvement project, said it was concerned about the standard of the work being carried out on the building that set alight on Monday.

"Workers sweating on the fire-stricken building were mainly from Henan province," an anonymous laborer who claimed to be a co-worker of the detained welders told the Economic Observer.