What are the statistics showing that the use of camouflage clothings
in the military has decreased the number of deaths?

Just go ahead and give up, you will never get an answer because it is
an impossible questions.  You would have to compare deaths while in
camaflouge and deaths where camaflouge didn't exist and that is an
impossible task.  A better question, something that would have an
answer, is asking to what extent the various military agencies have
determined that various camaflouge decreases a persons visibility in
various situations.