Is it obligatory to kill an apostate if he does not declare his apostasy or if he flees, and is it permissible for just anyone to kill him by chance?

One who apostatizes, but whose apostasy is not known, is outwardly considered a Muslim and treated as such. If his apostasy becomes known, he should be advised and called to repentance. If he persists, his case should be referred to the Sharia court. Individuals are not permitted to kill him or to carry out the prescribed punishment (حد) upon him. For the prescribed punishments are only carried out by the ruler (Sultan) or his deputy, to prevent chaos. "And it is not for anyone to remove an evil with something that is more evil than it."