Actually those guys are called Silver Guards. They take the role of da police and MES (EMERCOM, Emergency department, etc, my English lacks such knowledge).

Rank I is a regular policeman.

Rank II is the policeman that usually takes part in serious operations and other stuff like that.

Rank III is a special policeman, has more armor and better weapons. They lead operations, participate in hard operations, etc.

Detective is.. uh... detective?