Obama has said reforming the complex U.S. criminal justice system to reduce the number of people serving long sentences for non-violent drug crimes is one of the top priorities for his remaining time in office.
"Their punishments didn't fit the crimes," Obama said of those whose sentences he commuted in a video statement on Monday.
Obama said he hoped to work with a bipartisan group of lawmakers on criminal justice reforms. But so far legislative fixes have stalled in Congress.
With only 5 percent of the world’s population, the United States accounts for about 25 percent of the world’s prison population, according to the American Civil Liberties Union.
The Justice Department launched a program in April 2014 to systematically identify prisoners serving time for crimes they were sentenced for under laws that have since been changed to carry less severe punishments. Traditionally, presidents have granted pardons or commutations on a one-off basis.
Justice Department officials estimated the review would affect thousands, especially crack cocaine offenders sentenced when the drug still carried a sentence equivalent to someone caught with 100 times the same amount of powder cocaine.
But lawyers tasked with reviewing applications for reduced sentences say the complexity of the cases, and high number of applications, caught them off guard and created a backlog.
“The response was overwhelming,” said Cynthia Roseberry, director of Clemency Project 2014, which works with volunteer lawyers to process applications for the Justice Department to consider.
Roseberry’s team received 18,000 applications in the first two weeks of the clemency initiative. They have now received 30,000 and determined 13,000 failed to qualify.
Roseberry said lawyers were now racing against the clock to review as many applications as possible before Obama leaves office in early 2017.
Applicants qualify only if they have no record of violence, no significant ties to a gang or drug cartel, have been in prison at least 10 years and have demonstrated good behavior while incarcerated.
Only very recently has the review process started running effectively, said George O'Connell, a California-based former U.S. Attorney now providing pro bono legal assistance to prisoners.