As a result of the AIDS epidemic, there has been considerable expansion in research targeted at inner-city drug-using populations. Anthropology has played an important role in the effort to better understand HIV risk behaviors among drug users and to develop empirically grounded interventions. However, the study of highly vulnerable and social stigmatized populations raises important ethical issues, including the full extent of researcher responsibility to the subjects of research. This paper uses a case study approach to explore these issues. The case in question is a research participant who was killed by police in what they describe as a "police-assisted suicide" not long after his last interaction with research staff. The paper seeks to initiate discussion among researchers, funders, providers, and policy makers concerning key ethical and responsibility issues in HIV/AIDS research.