Some historians, and people that study the holocaust say that the true number of Jews killed was not anywhere near 6 million, more like 1 million if I recall correctly.
Anyway, I really have no idea how many were killed, but i't probably happened none the less.
The definite number of those killed in WWII IMO wont be solved, but even if it was more like 1 million, that is still 1 million people.