The remaining piece of the Riga Maxima supermarket roof fell in on Saturday evening.
The section of roof had remained intact but fragile since the first collapse on Thursday.
Fire and Rescue Service workers were immediately recalled from inside to ensure there were no further casualties.
The total death toll might be higher than 54, as there are still seven people missing.
The ambulance chief says the chances of finding more survivors was “close to zero”.
President Andris Berzins spoke bluntly about the disaster in an
interview with Latvian television.
“This is an event where we must clearly say that this is a large scale murder of many defenceless people and act accordingly. While not undermining the professionalism of our builders, I believe that we should call upon international expertise which is in no way connected with our construction business,” he said.
The exact cause of Thursday’s roof collapse is unconfirmed, but the focus has turned to a rooftop playground and garden that was being installed.
Many people gathered near the ruins on Saturday, bringing candles and flowers.