David Hercik, 2, looks Sunday at the candles and flowers placed as a memorial for Polish President Lech Kaczynski and his wife, Maria, at the gate of the Polish Embassy in Washington.

WARSAW, Poland — Russian investigators said there were no technical problems with the Soviet-made plane that crashed and killed the Polish president and 95 others over the weekend, suggesting pilot error may have been to blame.

The Tu-154 went down while trying to land Saturday in dense fog near Smolensk airport in western Russia. All 96 passengers and crew aboard were killed, including Poland's President Lech Kaczynski and dozens of political, military and religious leaders.

They had been traveling in the government-owned plane to attend a memorial at nearby Katyn forest honoring thousands of Polish military officers who were executed 70 years ago by Josef Stalin's secret police.

The pilot had been warned of bad weather in Smolensk, and was advised by traffic controllers to land elsewhere — which would have delayed the Katyn observances.

Russian investigators have almost finished reading the flight recorders, Deputy Prosecutor General Alexander Bastrykin said.

"The readings confirm that there were no problems with the plane, and that the pilot was informed about the difficult weather conditions, but nevertheless decided to land," Bastrykin said during a briefing with Russian Prime Minister Vladimir Putin in Smolensk. Bastrykin said the readings would be double checked.

The wreckage, meanwhile, will remain on site through midweek to help speed the investigation, Russian Deputy Transport Minister Igor Levitin said.

Both Russia and Ukraine declared a day of mourning today, as Poles struggled to come to terms with the national tragedy that eliminated so many of their government and military leaders.

Tens of thousands watched as Kaczynski's body, returned Sunday to Warsaw, was carried in a coffin by a hearse to the presidential palace. Forensics experts were working to ID other bodies.