Updated

President Barack Obama on Tuesday cut prison time for a drug convict sentenced to more than three extra years because of a typographical error in a court order.

White House counsel Kathryn Ruemmler said Obama's commutation of Ceasar Cantu's sentence from 15 to 11 1/2 years demonstrates "the importance of clemency as a fail-safe mechanism" for worthy inmates who run out of options. She said Obama has directed the Justice Department to improve its clemency recommendation process and recruit more applications from convicts.

"The president believes that one important purpose can be to help correct the effects of outdated and overly harsh sentences that Congress and the American people have since recognized are no longer in the best interests of justice," Ruemmler said in remarks prepared for delivery Tuesday at New York University's law school. "This effort also reflects the reality that our overburdened federal prison population includes many low-level, nonviolent offenders without significant criminal histories."

Cantu is only the 10th inmate Obama has granted a commutation, and his case was unusual. He pleaded guilty to drug trafficking and money laundering after prosecutors said he used his Houston trucking company to help move tons of marijuana from Mexico through Texas and into Virginia.

He was sentenced in Danville, Va., in 2006 by U.S. District Judge Jackson Kiser, who based his decision on a pre-sentencing report that had a critical error in "base offense level" that takes into consideration the crime's severity and the defendant's criminal history to come up with a sentencing guideline. The report correctly listed Cantu's level at 34 in one part, but incorrectly listed it at 36 in the portion that calculated a recommended  sentence of up to nearly 22 years.

Kiser noted at sentencing that although Cantu didn't have a criminal record, the quantity of drugs involved in his case deserved a sentence within the recommended guidelines. The judge told Cantu the best he could do was sentence him at the bottom of the guideline. But if the calculation had been correct, the bottom of the guideline would have been 3 1/2 years less.

"None of us made that connection in seeing the difference," Cantu's former attorney, John Weber, said in a telephone interview Tuesday after Obama's announcement.

Cantu said he didn't discover the mistake until 2012 when he received a copy of the presentencing report, and he accused Weber of ineffectively representing him. "By failing to object to this clear error, a manifestly unjust and prejudicial sentence was entered in my case," Cantu wrote in a motion he personally filed from Louisiana's Oakdale prison, where he is serving his time.

Kiser rejected Cantu's motion last year because it wasn't filed within the one-year statute of limitations. "While I am sympathetic to petitioner's position, I am not permitted to disregard the law," Kiser wrote.

The White House said Obama decided to grant clemency because it was the only way to correct the mistake.

"The extraordinary and unusual remedy of commutation may be used in certain instances to restore a degree of justice, fairness, and proportionality to an individual case," Ruemmler said in the remarks prepared for the keynote address at an NYU Law conference.

Obama commuted only one sentence in his first term, causing critics to charge that he was being too stingy with his power. Last December, Obama cut time for eight defendants sentenced under old guidelines that treated convictions for crack cocaine offenses harsher than those involving the powder form of the drug. Critics blamed the disparity for longer sentences being handed to black convicts, and Obama changed the sentencing standards for future cases beginning in 2010.

Ruemmler said the administration believes there is a larger pool of meritorious candidates for both pardons and commutations, and encouraged both types of applications. A pardon forgives a crime without erasing the conviction, typically after the sentence has been served. A commutation leaves the conviction and ends the punishment.

Ruemmler, who is preparing to leave the White House as soon as her successor is named, said the Justice Department plans in the coming weeks to encourage worthy inmates to request commutations, with bar associations offering to help with applications. She said Obama's new budget proposal calls for seven more staffers to be added to the Office of Pardon Attorney to handle applications, saying that the two years the office has taken to resolve petitions in recent years has been "unacceptably long." She said Obama met with U.S. attorneys last month and asked them to personally review petitions to consider "whether granting clemency would be consistent with the values of justice and fairness that are the hallmark of the best traditions of the Department of Justice."