Halakhah zu Mischlej 29:4

The root of this commandment is revealed to all, as 'by justice a king sustains the land.' As were it not for the fear of judgment, people would kill one another. Therefore, God, blessed be He, commanded us to kill the murderer. And in His wisdom, blessed be He, He saw that it is fitting to punish him with the death penalty of strangulation. And the matter is beautiful, also according to our [understanding], since 'as he has done, so shall it be done to him' - since the intention of the killer was to kill the murdered quickly, as from [the killer's] fear of him, he will quicken his death with all of his might. And so too was the Torah lenient with his judgment to kill him with strangulation, which is a quick death penalty; and not with stoning and burning, which are with great pain. (In the other editions, it is written, "The truth is that the death penalty of the murderer is with the sword, [whereas] he who hits his father and mother has a death penalty of strangulation.") However with the statutes of licentiousness, in which the transgressors derived pleasure from the sin and the pleasure continued a bit, they sometimes get burning and sometimes stoning.

From the roots of this commandment are to punish scoundrels and informers that raised their hand against the ones that brought them to the world by the will of God and did for them many goodnesses. And 'by justice does the King sustain the land.'