If a murdered body is found and the crime cannot be solved, the city closest to the body must perform the ceremony of eglah arufah found at the end of our parsha. The Netzi"v quotes a machlokes Bavli and Yerushalmi regarding the meaning of the declaration by the Zekeinim that "eineinu lo ra'u". The Bavli interprets the pasuk to mean that the Zekeinim were not aware of the victim; they did not knowingly ignore a stranger in their midst and send him off wandering alone in the wilderness without offering proper hospitality and a place to stay. The Yerushalmi, however, interprets the declaration to mean the Zekeinim were not aware of the murderer; they did not knowingly ignore a criminal in their midst and allow him to continue to prey on the innocent.
The Netziv suggests a nafka minah between the two approaches. The measurement to determine which city is closest only takes into consideration cities which have a Beis Din. What type of Beis Din is required? According to the Bavli, it would seem any Beis Din of three is sufficient. However, according the the Yerushalmi that reads the pasuk as addressing itself to Zekeinim who could punish a murderer, a Beis Din of twenty-three capable of carrying out capital punishment is required. The Rambam paskens that a B"D of 23 is needed.
The halacha is that the ir miklat city of refuge must have Zekeinim in residence. The Minchas Chinuch (410) questions what type of B"D is necessary and suggests the law of eglah arufah which requires 23 as a point of comparison. Based on the Netziv's approach one can distinguish between the cases. The requirement of B"D by eglah arufah according to the Yerushalmi is a function of the necessity of being able to administer capital punishment; the same requirement is not needed for ir miklat.