How is it that God decided that the death of one could save the multitudes?

Was there no other way? If he is omnipotent, couldn't he have chosen to save us all with his supreme magic powers? Why did he make his only begotten son suffer an horrible torturous violent death just because we did exactly what he created us to do, which was use the free will that he gave us? How exactly does this one death make a baby rapist go to heaven if he just believes in its magical powers?