Thousands of nonviolent federal prisoners eligible for early release under a promising Trump-era law remain locked up nearly four years later due to inadequate implementation, confusion and bureaucratic delays, prisoner advocacy groups, affected inmates and former federal prison officials say.

Even the Biden administration’s attempt to provide clarity to the First Step Act by identifying qualified inmates and then transferring them into home confinement or another form of supervised release appears to be falling short, according to prisoner advocates familiar with the law.

The Department of Justice was tasked with carrying out the law through the federal Bureau of Prisons, but the bureau director, Michael Carvajal, a Trump administration holdover, announced his retirement in January amid criticism of a crisis-filled tenure marked by agency scandals. No replacement for Carvajal has been named, and criminal justice advocates contend that for the bureau to allow even one person to be incarcerated beyond what is permitted under the First Step Act exposes ongoing failures.