Warsaw , Poland -LRB- CNN -RRB- -- The body of Polish President Lech Kaczynski , who was killed in a plane crash in Russia over the weekend , returned to tributes in his homeland Sunday afternoon . Soldiers in perfect step carried the casket from the plane that transported onto the tarmac , where mourners were waiting . Catholic priests recited prayers at the military airport before Kaczynski 's daughter and twin brother , followed by others , took turns kneeling before the flag-draped casket . People lined up along the streets along where Kaczynski 's body would pass on its way to the presidential palace . Tens of thousands of Poles across the country observed a two-minute-long moment of silence to remember their president and 95 others killed in the plane crash . iReport : Mourners ' candles a ` spot of light ' Meanwhile , investigators said they found the aircraft 's flight data recorders in good condition and began deciphering them Sunday , the independent Russian Interfax news agency reported . Residents flocked to central Warsaw , the site of the presidential palace , to mourn Kaczynski . They left wreaths and lit candles . By Sunday , the numbers grew to about 100,000 by some estimates . Many cried openly . Others stared blankly at the sky . On Monday , the country begins a week-long period of mourning . The plane carrying Kaczynski crashed Saturday morning while trying to land at an airport near Smolensk in Russia . Biography : Lech Kaczynski Kaczynski 's wife and several top military officials were also killed in the crash . Parliament Speaker Bronislaw Komorowski took over as acting president and declared it `` a time for national mourning . '' Kaczynski , 60 , had been traveling with a Polish delegation to Russia for the 70th anniversary of the Russian massacre of Polish prisoners of war in the village of Katyn . About 20,000 Poles , including soldiers and civilians , were executed there during World War II . The Polish military plane carrying Kaczynski originated in Warsaw , the Polish Defense Ministry said . It was just a few miles east of Katyn when it crashed around 10:50 a.m. -LRB- 2:50 a.m. ET -RRB- on the outskirts of the town of Pechorsk , close to Smolensk , the Investigation Committee of the Russian prosecutor 's office said . World leaders pay tribute to Kaczynski Late Saturday night , Kaczynski 's twin brother , Jaroslaw , visited the site of the crash . As others around him prayed , he silently knelt down on pile of rubble where mourners had propped up flowers . Authorities do not yet know what caused the crash . Russia has emphasized that there is no evidence it was responsible . The Investigation Committee said the plane , a Tupolev-154 , was trying to land in heavy fog . A Russian military official said that air traffic control in Smolensk had tried to divert the plane to another airport because of inclement weather . `` The air traffic control officer gave several orders to divert but the plane continued with its descent , '' said Alexander Aleshin , a top Russian air force official . `` Unfortunately , this ended in tragedy . '' Russian President Dmitry Medvedev appointed Putin to head an inquiry commission . On Sunday , the Russian state-run RIA Novosti news agency reported that the crash was not caused by technical problems , citing investigation officials . The plane carrying Kaczynski was refurbished and repaired last year , according to Alexei Gusev , general director of Aviakor Factory , the company that performed the service . `` Speaking openly , we believe that this tragedy could not have been caused by equipment failure , '' he said . Kaczynski had been president since December 2005 , after he defeated rival Donald Tusk in the second round of voting . Elections must now be held within 60 days . Other Polish officials killed in the crash include Aleksander Szczyglo , the head of the National Security Office ; Jerzy Szmajdzinski , the deputy parliament speaker ; Andrzej Kremer , the deputy foreign minister ; and Gen. Franciszek Gagor , the army chief of staff , according to Kaczynski 's Law and Justice Party . What does crash mean for Polish politics ? The party also said that Slawomir Skrzypek , head of the National Bank of Poland , was killed . Putin spoke Saturday at the crash site , where charred pieces of the airplane were strewn through a wooded area . Some pieces , including one of the wheel wells , were upside down . `` As our first priority , we must establish the causes of this tragedy , '' he said . `` As a second priority , we must do everything in our power to assist the families and relatives of the deceased . '' CNN 's Frederik Pleitgen in Warsaw , Poland , and Nic Robertson in Smolensk , Russia , contributed to this report .