Soldiers imply that they were just typical casualties of war, but this was different, it basically plain mass murder of mostly civilians.
After the Soviets invaded Poland in 1939 they captured about 8,000 officers, 6,000 police personnel and about 8,000 intelligentsia (educated people like professors, writers, scientists, engineers, lawyers etc) basically any that could lead and be a problem for USSR.
They then murdered all of them in woods in Katyń.
Things like these are why Poland and also other Baltic states are so fiercely against Russia.
