In August 2014, Judge Julie Robinson, then chair of the Court Administration and Case Management Committee (CACM), asked the Federal Judicial Center (FJC) to conduct a study to determine the number of offenders harmed or threatened with harm because they cooperated, or were suspected of cooperating, with the government. The population of concern included inmates who were post-conviction and in the custody of the Bureau of Prisons (BOP) and identified as cooperators through the use of court documents. The request, made on behalf of CACM, the Criminal Law Committee, and the Committee on Defender Services, asked that we survey federal defenders, Criminal Justice Act (CJA) panel attorneys, federal prosecutors, and probation officers and ask them to report the number of offenders harmed or threatened with harm. We added district judges, witnesses, pretrial services offices, and pretrial detention to the study design as a result of early discussions with staff from the Administrative Office of the U.S. Courts (AO staff).