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ДЕТЕКТИВ - an expert on the criminal investigation, detective, detective. His responsibilities include the collection of evidence and giving their jurisdictions.
Private investigator - a person performing a detective (detective) activity and detective services provider in private (individual) way.
МЭР - head of administration, chief executive of the village, most of the city, in some countries - and a small region, such as Lithuania, mayor heads and district governments.
Job title comes from the Latin word «maior», meaning "big", "great". In Russia, the title stuck in the 1990s, more like a short replacing the phrase "mayor", "the head of the city administration," or "head of the city executive committee." In this case, the position of "mayor" was introduced at the official level