who were those people

They were the conscience of Poland.
The incorruptible ones who had defied, and prevailed, over first Nazi Germany then Communist Russia.
The liberators who by the grace of God had repudiated Soviet dictatorship though a lifetime of heroic courage and witness to the truth.
The ones who had thwarted the best efforts of resovietising psychotics to once more subvert and enslave their nation.
The ones who could spot an agent in the pay of Vladimir Putin at five hundred paces on a dark night with no moon.
Yes, these were the incorruptible ones.
Guardians of the soul of the Polish nation.
That is why they were murdered.