Inspector Javert is one of those characters who defines "blind justice." Stoic and implacable in the latest version of Les Miserables gracing movie screens across the country, his immortal line has sent shudders through readers and audiences alike for a century and a half: "It is a pity the law doesn't allow me to be merciful." Such is the power of his symbolism that today, our laws allow just the mercy that Javert denied. However, putting mercy into practice is a challenge.

Charles Costanzo is one of the lucky ones. He benefited from a law passed in 1984— call it Javert's law — that says courts may release federal prisoners in "extraordinary and compelling circumstances" upon motion by the federal Bureau of Prisons. Diagnosed with Stage 4 stomach cancer while serving 70 months for embezzlement, Costanzo was able to spend his last days at his mother's home.

Congressional compassion

Congress recognized that situations arise that make continued incarceration senseless and inhumane. Old age could so whittle a prisoner's body that he cannot dress, eat or bathe by himself. The accidental death of a prisoner's husband might condemn young children to foster care.

Unfortunately, the bureau is reluctant to make motions for "compassionate release." We do not know how many prisoners seek compassionate release each year because the bureau does not keep count. But in 2011, for example, when there were about 218,000 federal prisoners, the bureau said yes only 30 times. Since 1992, it has made motions about two dozen times a year.

Why so few? In part, it's because the bureau will not make a motion unless the prisoner has fewer than 12 months to live or is utterly and irrevocably incapacitated. Yet even then, it may say no.

Take Michael Mahoney. He was sentenced in 1992 to a mandatory minimum term of 15 years for possessing a firearm following three drug-dealing convictions. In 2004, he developed lymphoma. Dying, passing in and out of consciousness, he sought compassionate release. Citing Mahoney's prior convictions, the agency rejected his request. Mahoney died shortly thereafter.

Legitimate concerns?

The bureau denies compassionate release for many prisoners because, in theory, they are still capable of re-offending regardless of whether it is likely. It also considers whether a prisoner has, in the judgment of wardens and more senior officials, been punished enough, whether release might depreciate the seriousness of the crime or whether the crime was just too heinous.

But Congress left those judgments to courts. The bureau is supposed to serve as a screen, making sure, for example, that a prisoner is actually dying. The Bureau of Prisons has usurped the judicial function by making its own decisions about whether compassionate release is warranted. If the bureau decides against the prisoner, the courts' hands are tied because they have no authority to hear the prisoner's motion. The jailer has become the judge.

It might not be surprising that the bureau, part of the Justice Department, is reluctant to help prisoners secure an early release. The Justice Department makes tough sentences a priority and is not keen on having courts reconsidering them. That's why courts should be allowed to play the role that Congress gave them.

Jamie Fellner is an adviser to Human Rights Watch. Mary Price is vice president of Families Against Mandatory Minimums.