ICPSR recently announced an update to its Capital Punishment in the United States, 1973-2004 dataset (ICPSR Study No. 4430). (I've worked with prior versions.) The dataset is put together and maintained by BJS (part of DoJ); ICPSR is the repository. A summary of the dataset follows:
"This data collection provides annual data on prisoners under a sentence of death and prisoners whose offense sentences were commuted or vacated during the period 1973-2004. Information is supplied for basic sociodemographic characteristics such as age, sex, education, and state of incarceration. Criminal history data include prior felony convictions for criminal homicide and legal status at the time of the capital offense. Additional information is available for inmates removed from death row by year-end 2004 and for inmates who were executed."
In addition to the data and necessary documentation (e.g., codebook), ICPSR also makes available ready-to-use SAS, SPSS, and Stata files. Even those wholly uninterested in these data might wish to familiarize themselves with ICPSR's holdings. ICPSR is a veritable treasure-trove for empiricists, including, increasingly, legal empiricists.