Latvian Prime Minister Valdis Dombrovskis is resigning in the wake of a deadly supermarket roof collapse, his spokesman said...The roof collapse...in...Riga, left more than 50 people dead -- the deadliest incident in Latvia since the country became independent in 1991...A total of 54 people, including three firefighters, died in the collapse and several dozen were injured, LETA said...President Andris Berzins told Latvian television that "nature could not be blamed" and that those involved needed to think about what they had done, so that action could be taken...The cause of the disaster is still under investigation. However, Riga Mayor Nils Usakovs told CNN last week that authorities think building materials stored on the roof caused it to collapse.