That frequency is part of a wide area network of repeaters in southern Arizona, part of the federal Integrated Wireless Network (IWN). It's used mainly by the Customs & Border Protection (CBP) and Immigrations & Customs Enforcement (ICE). The DEA certainly could be using it as well, probably in a joint operation with ICE.
Different repeaters use different P-25 NACs, so they are not assigned by agency, but by the repeater location and which input the users are using.
- Chris