With no due process? An on the spot death penalty in a country with no legal death penalty? There should be some sort of process at least to identify someone and to give this person the chance for a defense.
The proposed solution is worse than the problem and the vermin are the vigilantes.
Another issue is that in a land where law enforcement resources are in short supply, this becomes a genie which is difficult to stuff back in the bottle. Once vigilanteeism becomes accepted, then it will be hard to stop in the future.