By Chris Lau, Karina Tsui, Rhea Mogul, CNN

Hong Kong (CNN) — Hong Kong’s leader said he will ensure “justice is served” over the inferno that killed more than 150 people last week, as city officials point the finger of blame at construction companies for allegedly using substandard mesh netting to wrap scaffolding on the buildings.

Tuesday was the seventh day after the first deaths –– an important day in Chinese tradition as it’s believed to be when the soul of a deceased loved one returns to visit the family home. Hundreds of mourners made an emotional pilgrimage to the scene of the fire to mark the occasion by praying and laying flowers.

At least 15 people have been arrested over the blaze, which tore through seven high-rise apartment blocks and burned for almost two days, and more arrests may follow, authorities said, with the city’s chief executive John Lee vowing to “uncover the truth” and “pursue justice” for the dead.

“I will initiate an independent committee, led by a judge, to investigate the reason the fire started and how it spread so fast,” said Lee, who promised “systematic reform”.

“No matter who is involved we will get to the bottom of it,” Lee said.

The death toll rose to 156 people on Tuesday, with 30 still missing, after the city’s worst fire in decades tore through the Wang Fuk Court complex. The housing complex, which was undergoing renovations, was home to more than 4,000 people, many of whom were elderly.

Most of those arrested are consultants, contractors or subcontractors connected to the construction work. Of those arrested, 15 people, 14 male and one female, are being investigated on suspicion of manslaughter by way of gross negligence, officials said.

A painstaking search effort for the remains of the victims continues at the site, with specialists meticulously combing each apartment.

Substandard netting

Substandard mesh netting that was wrapping bamboo scaffolding around the complex towers and did not meet fire safety standards contributed to the rapid spread of the blaze, officials said Monday.

Seven of 20 samples taken from the complex after the fire had failed fire safety tests, said Hong Kong’s Secretary for Security Chris Tang.

Woo Ying-ming, the city’s corruption commissioner, said the netting around the building had been damaged during a typhoon in July and accused the group of purchasing non-compliant netting to replace it. “They applied it on the damaged spots,” said Woo, who added that officials had calculated they had bought enough to wrap all eight towers at the complex.

Fearing the netting would be examined after a fire at another Hong Kong high-rise in October, the group allegedly purchased more fire-safe netting that they wrapped only around the ground floors one the buildings, said Woo.

“The suspects are very cunning,” said Chief Secretary Chan Kwok-ki. “For very little profits, they take the lives of many people.”

Polystyrene boards that were used by contractors to block windows at the complex have been identified as another factor that contributed to the speed of the inferno’s spread. Officials said they had identified three other building sites in the city where the same technique was being used and asked for the boards to be removed.

Important day of mourning

In a public square next to housing complex on Tuesday, mourners from all over Hong Kong waited in an orderly line to lay flowers and offer prayers and well wishes to the victims. Some sobbed as they stood on the sidelines of the growing memorial.

Lying next to the sea of flowers were offerings of fruits and the favorite snacks of the deceased –– left there by those who believe their loved ones could still enjoy their much-cherished treats in their afterlife as they returned to their homes on the seventh-day.

Volunteer Sarah Lam traveled across the city to Wang Fuk Court to lead some of Tuesday’s memorial efforts.

“A lot of people have been telling me they feel hopeless and helpless but I tell them ‘no, there’s actually a lot you can do, you can help us remember them.’” she told CNN.

A woman in her 50s packed a day’s worth of food, snacks and water and planned to stay for as long as she could to mourn the victims who, she said, died in a “senseless tragedy.”

“It’s so painful to be here but I just can’t bring myself to leave,” the woman who identified herself as Miss Chan told CNN.

Another man, who works at a flower shop, was cutting and handing out blooms to mourners trickling in.

Search continues

An estimated 600 disaster victim identification specialists have been slowly going door to door to clear each apartment since the fire was extinguished Friday.

“Since some of the bodies have been reduced to ashes, we don’t rule out that we may not be able to bring all the missing people out,” said Chief Superintendent Karen Tsang, head of the casualty inquiry unit, who fought back tears during a press conference on Monday afternoon.

Images released by police showed boiler-suit-clad searchers carefully checking through the ashes of burned belongings inside a fire-ravaged unit. The complex task is made harder by dim lighting conditions and narrow corridors blocked by fallen objects, police said.

“During the search, bodies were found in the building corridors, flats, staircases, and even on rooftops,” said police superintendent Cheng Ka-chun, who led the specialist police identification unit.

By Monday night, the search had concluded at five of the towers, but officials said some apartments in the remaining two damaged blocks were structurally unsafe for searchers to enter.

Those killed included a number of elderly residents, foreign domestic workers who lived with their employers – many of whom are older people or families with children –– construction workers and a firefighter who had been deployed to the scene.

Nine of the domestic workers were from Indonesia and one was from the Philippines, their consulates said.

National security arrests

Some aspects of the community response have drawn suspicion from authorities, who have warned against a resurgence of anti-government sentiment in Hong Kong, referencing pro-democracy protests that broke out in 2019.

Hong Kong is a semi-autonomous part of China and run by its own local government that answers to leaders in Beijing.

On Saturday, Beijing’s national security office in the city warned against any renewed dissent, calling for the city’s government to punish those wishing to use the fire as a pretext to “oppose China and stir chaos in Hong Kong.”

National security police have since arrested three people, including one detained on suspicion of incitement after allegedly distributing materials in support of an online petition calling for an independent enquiry into the fire, among other demands, their lawyers told CNN.

“We will not tolerate any crime, particularly crimes that exploit the tragedy happening to Hong Kong,” said Lee, the chief executive, on Tuesday.

The petition, which has since been removed, had over 10,000 signatures by Saturday afternoon, Reuters reported.

A pro-Beijing newspaper reported that a high-ranking Hong Kong police superintendent in charge of national security also visited the site of the fire.

Authorities have asked volunteers to leave the fire scene, announcing that it would centralize the distribution of resources and require people to register through WhatsApp for their donations.

This article has been updated with additional information.