There are many people swear falsely so why in islamic rule court can order base on swear to koran ?

i have seen many lifes change just because of false swear of some people but still in islamic country many court orders is base on swear . if 4 person swear falsely that a man has killed some one accordding to islamic laws that helpless man should be punish . please dont write me that there is such a rule in other religions i am not here to compare islam with another religions . this is just a question about islam i want to know if islam is the most complete religion what should be so ?????????no wise accept that there are always many people in islam religion or other religion who lie so how can trust to swear ????????dont you agree many people swear to koran falsely ????so if islam says court can trust to swear to koran its cant be true