Both sources report data provided by medical examiners for the fourArizona border counties: Pima County, Santa Cruz County, Yuma County, and Cochise County. The majority of the Arizona deaths occur in Pima County.
Not all the dead are identified. On trends in the number of unidentified bodies, see this press release from the Coalición de Derechos Humanos.
For the border region as a whole, yearly estimated death counts range from the 300s (around one per day) to the 800s (over two per day), depending on the year and the method of counting. See the A.C.L.U. report Humanitarian Crisis: Migrant Deaths at the U.S.–Mexico Border (October 2009) for sources. A complete list of people who have died while crossing the border does not exist, and will probably never exist.
The annual number of migrant deaths shows no signs of decline, but there is also strong evidence that crossing the border has become substantially more dangerous from year to year.
The best available measure of the risk of death is the ratio of recovered bodies to Border Patrol apprehensions in a given region and time period. In the Border Patrol's Tucson Sector (which covers the Arizona border counties, excluding Yuma County), in fiscal year 1998, there were 3 known deaths per 100,000 apprehensions.
By contrast, there were 88 known deaths per 100,000 apprehensions in fiscal year 2009—a thirty-fold increase in eleven years. See Risk of Death Higher Than Ever for Migrants and the Arizona Daily Star article cited therein.
That trend continued in fiscal year 2010, with 253 known deaths and 219,318 apprehensions (Arizona Daily Star, Dec. 18, 2010). The ratio is an unprecedented 115 known deaths per 100,000 apprehensions.