The answer to the third question is that the death sentence can only be given to a person who has killed someone or to someone who is guilty of spreading disorder in a society. No other person can be punished by death. The Qur’ān says:
مَنْ قَتَلَ نَفْسًا بِغَيْرِ نَفْسٍ أَوْ فَسَادٍ فِي الْأَرْضِ فَكَأَنَّمَا قَتَلَ النَّاسَ جَمِيعًا (32:5) He who killed a human being without the latter being guilty of killing another or of spreading anarchy in the land should be looked upon as if he had killed all mankind. (5:32)
This is the verdict of the Qur’ān. Hence, except for these two offences, neither a person nor an Islamic government has any right to administer the death sentence to a person.