A law review article, by Brandon Garrett, Alexander Jakubow and Ankur Desai, presenting statistical analysis of these findings is available here. That analysis includes county-level data on demographics and homicides by county.
An Excel spreadsheet version of this database is available here. A coding sheet accompanying that analysis is available here. A separate article, by Brandon Garrett and Ankur Desai presents state-level analysis of these data and is available here.