In his weekly islahi lecture sayyidi wa sanadi Shaykh Mohammad Taqi Usmani (Allah preserve him) reminded us,
‘There are no circumstance under which it is permissible for individuals to take law in their own hand to punish those who commit major sins or turn apostate. It is the task of the government administration to apprehend them.
Killing non-Muslims (dhimmis) living in a Islamic country is as haram (impermissible) as murdering a fellow Muslim.
To emphasize the significance of this it is reported in a saying of the Prophet (Allah bless him and give him peace) that the peron who kills a non-Muslim (dhimmi) living in a Islamic country will not even smell the fragrance of Paradise (which is so strong that it can be smelt at a distance of 500 years).
More explicitly he (Allah bless him and give him peace) admonished the Muslims at his last Hajj, to not to become like non-Muslims killing one another.’