According to the source, an external video surveillance system recorded the moment of the tragedy. The recording is clear as it was already dark outside, and the building was brightly lit inside.

One of the columns in the left part of the complex collapsed, pulling with it part of the roof. That column was not the tallest, there were taller columns near the center of the building. The collapse set off a chain reaction, and columns collapsed one after another like a house of cards. The huge domed roof caved in a matter of a few seconds.

There was a cloud of dust near the ill-fated column, about 1.5m above the ground, which was suspected as a possible point explosion. But the source in the Prosecutor’s Office said it did not look like an explosion. In his opinion, the pillar deformed in the process of collapsing, and the plaster came off. A thorough technical examination is being carried out.

According to prosecutors, the collapse of a small pillar should not lead to the collapse of the whole roof. Such large leisure facilities should be built more securely.

The source said there could also be other mistakes, apart from a flawed roof design, such as construction mistakes and poor quality material. In his opinion, the collapse could have been caused by ground movements. But he said no cracks had been found in the foundations of the building during a preliminary examination. If there had been ground movements, there would have been cracks.

According to the Kommersant newspaper, five commissions are investigating the incident. Three of them were set up by the Moscow Prosecutor’s Office, the Moscow administration and the State Construction Committee. There is also a team of scientists and an independent panel of Canadian construction experts. In addition, the Federal Security Service is investigating a possible terrorist attack.

Prosecutors will examine the column that collapsed first. The foundations of the complex are being examined. The examinations will be completed by March 9. But it has already been established that the most likely cause of the incident is a flawed column design.

The origin of the cloud of dust, which was recorded by the external video surveillance system, has not been established yet. It looks rather strange. It can be seen from both inside and outside the building. It is unclear whether it was outside the building and reflected in the window or vice versa. But it was at the moment the cloud appeared that a bang was heard in the building, the Kommersant says.