It may have won Latvian Building of the Year after it was completed in 2011, but there were clearly fatal flaws in the roof of Riga's Maxima supermarket, which collapsed at the end of last month killing 54 people and injuring another 39.

As the fallout continues – Latvian Prime Minister Valdis Dombrovskis has already resigned over the incident – fingers have been pointed at the structural design of the building.

Although authorities are still considering that the cause may also be related to initial building procedures or the construction of the supermarket’s green roof, Toomas Kaljas, a structural engineer working for a Finnish company, has suggested the connections between the horizontal bars that held the roof were inadequately designed. He says the garden on the roof, only part of which had been built, played a minimal role.

“The engineers were clearly negligent,” Kaljas has asserted.

He went on to explain that the load on the bolts that were holding the bars was uneven and there were too few of them.

“A better design would have resulted in components bending and cracking over time, instead of the whole building suddenly collapsing like dominoes without a warning,” he added.

HND Grupa, which was responsible for the construction of the building, admitted that trusses made of two pieces bolted together were used, rather than the single truss specified in the original design, due to difficulties transporting longer trusses to the building site

Such a change should have required that the entire design plan be revised and re-approved by authorities, according to Lilita Ozola, an engineer teaching at the Latvian University of Agriculture. She said that the joint between the two-piece trusses would bear most of the roof’s weight and that video footage of the disaster clearly showed failure at the exact position of the joints.

An anonymous fireman, who took part in the rescue effort, told TV3 News that the bolts he had seen on the scene had not been broken but instead pulled out from fastenings, indicating they were not designed to bear the weight of the roof.

An independent engineers’ report has now been released which says “shoddy errors” were made. Aldis Grasmanis, Valerijs Vasiljevs et Didzis Zigurs drew up their conclusions for the building company Re&Re after studying construction documents. They have stated that the main reasons for the collapse were faulty estimation of the maximum load to be carried by the roof and the design of the connections in the structural steel supporting the roof.

Re&Re has also invited international construction engineering company BRE Global to carry out a full analysis and examination of construction materials at the Maxima supermarket once the facility is accessible again

According to Maxima staff, the building had been dangerously unstable for about a year, with construction workers telling them that the foundation was cracked and required reinforcement. There had also been extra support columns under the ceiling of the storage room which were subsequently been removed.

The investigation continues. In the meantime, the Mayor of Riga Nils Ušakovs has said that the Maxima building will be demolished and a memorial built in its place.