Federal public defender Paresh Patel’s office is crowded with hundreds of petitions filed for inmates seeking early release because of a Supreme Court decision last year. (Marvin Joseph/The Washington Post)

Hundreds if not thousands of federal prisoners are likely to have their sentences shortened — and in some cases get immediate release — due to one of the final opinions written by Justice Antonin Scalia.

Scalia’s little-noticed opinion focused on one phrase in federal law but has created uncertainty and upheaval for judges, prosecutors and defense attorneys facing a pile of prisoner requests to have their cases reviewed.

Federal inmates have until Sunday to try to challenge their prison terms after the Supreme Court labeled 12 words in the criminal code “unconstitutionally vague” in an opinion announced by Scalia last June, eight months before his death.

The ruling eliminated a section of law that prosecutors relied on to seek stiffer penaltiesfor defendants they said were especially dangerous. Defense attorneys had decried the wording because it was used to brand too many defendants as violent.

U.S. Attorney Rod J. Rosenstein in Maryland has had to hire two new attorneys to help respond to the hundreds of petitions from federal inmates seeking early release. (Michel du Cille/The Washington Post)

This wave of sentencing appeals across the country coincides with separate efforts by reform advocates to roll back decades of lengthy, mandatory prison terms created during the nation’s war on drugs. President Obama has commuted the sentences of nearly 350 people.

Unlike the low-level, nonviolent inmates the administration has targeted for clemency, prosecutors such as U.S. Attorney Rod J. Rosenstein in Maryland are concerned the new court ruling will lead to the early release of truly violent people. It also could be painful for victims’ families if sentences imposed years ago unravel.

“The finality for the families that we thought came with the appellate process is no more,” said assistant U.S. Attorney Debbie Dwyer, who is overseeing hundreds of sentencing petitions in Rosenstein’s office. “We don’t know when it will end. This makes the process seem endless.”

Rosenstein has hired two lawyers to help respond to requests to revisit more than 580 old cases, including one involving the kidnapping and murder of three women in Prince George’s County in 1996. He worries about the diversion of resources from prosecuting crime in Baltimore, which recorded nearly 350 homicides in 2015.

For defense attorneys, the court’s decision provides a new avenue to challenge lengthy sentences for prisoners who received severe penalties for nonviolent offenses, such as resisting arrest.

“It was a dumping ground,” said Amy Baron-Evans of the Sentencing Resource Counsel Project of federal public defenders. “It ended up sweeping in crimes that no one would think of as being violent.”

Filings from inmates are piling up in judicial chambers throughout the country. In Atlanta, one judge took the unusual step this spring of flagging the names of 110 prisoners from her district eligible to refile for shorter sentences to alert them to the deadline this month – one year from the date the Supreme Court decision was handed down.

In Richmond last month, the U.S. Court of Appeals for the 4th Circuit, which covers Virginia, Maryland, West Virginia, North Carolina and South Carolina, received more than 500 filings for sentence reviews, according to the clerk’s office. In the same period last year, there were 18.

More than 350 petitions have been filed in the 8th Circuit in St. Louis since May, contributing to a record number of filings in a single month.

The law at the heart of the opinion was passed in the 1980s to toughen existing punishments for felons with guns.

The typical sentence for a felon in possession of a firearm is 10 years. But in 1984, Congress passed the Armed Career Criminal Act, with a mandatory minimum of 15 years, to enable prosecutors to try to get people with guns and a history of violence off the streets by ratcheting up sentences.

The 8-to-1 Supreme Court opinion last year struck one piece of the act that the court said led to inconsistent, arbitrary enforcement and did not provide “fair notice” to defendants about which types of crime qualify as violent felonies. The phrase refers to “conduct that presents a serious potential risk of physical injury to another.”

That vague clause, the court said, “leaves grave uncertainty about how to estimate the risk posed by a crime.”

The court’s opinion cleared the way for inmates sentenced under the act to have their prison terms trimmed by at least five years. Prisoners are not asking for new trials but for another shot at sentencing by a federal judge.

Isaac Edwards was one of them.

In 2010, Edwards made a run for it after police caught a whiff of marijuana coming from his car during a routine traffic stop in Baltimore. Police nabbed him after a brief chase, then discovered a gun in a black handbag in the back seat. Edwards was charged as a felon in possession of a firearm.

To have Edwards face the mandatory 15-year prison term, prosecutors needed to show he met certain requirements. A defendant has to have three previous convictions for serious drug offenses or for violent felonies, or a combination of the two.

The law cites some specific crimes that qualify: burglary, arson and extortion. Other crimes qualify if the offense involves the “attempted use, or threatened use of physical force” against a person.

But the Supreme Court struggled during four earlier cases to offer better guidance to lower courts on what types of crimes counted under the law, finding that attempted burglary, for instance, was covered, but not drunken driving.

By the time Edwards was picked up after the traffic stop, he had two state drug convictions. The third strike against Edwards, now 31, was running from the police after being approached for loitering near a public housing unit in Baltimore in 2005.

Prosecutors argued that he should get the 15-year term because fleeing in the 2005 case amounted to conduct presenting a “serious potential risk of physical injury” as outlined in the problematic part of the law.

“If a prosecutor really wants to slam a guy with a long record, they have an interest in portraying any and every part of that history as qualifying,” said Douglas A. Berman, an Ohio State University law professor who writes the Sentencing Law and Policy blog.

“Defense attorneys say it’s been used in a technical way,” he said, “to get those who didn’t deserve to get slammed.”

Edwards’s attorneys challenged his sentence under the court’s new interpretation. Instead of serving a mandatory 15 years, a federal judge in Baltimore cut Edwards’s sentence in half. He will be released in December, his attorney said, after serving seven years.

The language overturned by the Supreme Court in the criminal code echoes in other parts of the justice system.

Nearly identical words about career offenders appear in federal sentencing guidelines, which use a formula to give judges a recommended range of possible prison time for the defendants who come before them.

Federal public defenders and the U.S. Justice Department agree that the Supreme Court ruling negates those words in the guidelines for defendants sentenced since Scalia’s 2015 opinion.

The Supreme Court separately is being asked to settle a dispute about whether inmates punished before the 2015 opinion should have another chance at sentencing.

The Justice Department says they should not, according to the government’s court filings. The judges who handed down those prison terms were not bound to a particular mandatory sentence and imposed what they thought were appropriate punishments that should stand, the government says.

To the public defenders, that position is at odds with the Obama administration’s advocacy for clemency. If the court rules that the decision does apply retroactively to the guidelines, another 6,000 federal inmates sentenced between 1992 and 2015 could ask to have their prison time cut, according to an estimate from the public defenders’ sentencing project.

Prosecutors say “the sky is going to fall and all of these violent people are going to be let out,” said federal public defender Paresh Patel, who is handling appeals for the Maryland office. “People are not getting a windfall. They were wrongly sentenced as career offenders.”

Justice Department spokesman Patrick Rodenbush said the administration’s position is “fully consistent” with its clemency efforts. The guidelines apply “only to individuals convicted of specific crimes of violence and are wholly distinct from grants of clemency to drug offenders who have been vetted for public safety concerns.”

Prosecutors worry about the ripple effects of Scalia’s opinion. Inmates and their lawyers argue that the court’s decision to eliminate words in one law should stick to other areas of law with parallel language. These filings raise new questions about what types of crimes meet the technical definition of a “crime of violence” and how judges assess a person’s criminal past.

In response to the Supreme Court’s decision, attorneys for Dustin John Higgs in May asked the 4th Circuit for permission to challenge his death sentence.

Higgs was sentenced in 2001 for ordering the murders of three young women in Beltsville. The women were shot to death on a desolate stretch of federal land near the Patuxent Wildlife Research Center. Higgs was convicted of using a firearm during a “crime of violence” — in this case kidnapping and murder.

Higgs’s attorneys are not saying he is innocent but that the court ruling means the firearms convictions are void because, without the problematic language, murder and kidnapping now “fail to categorically qualify as ‘crimes of violence.’ ”

In their court filing, Higgs’s attorneys say that murder and kidnapping “can be accomplished without the intentional use, attempted use or threatened use” of violent physical force.

Prosecutors say Higgs will not be released from prison any time soon because he will still be subject to the nine death sentences he received on the murder and kidnapping convictions, which are separate from the firearms charge.

Even if Higgs does not personally benefit, prosecutors say, a new interpretation in his case could upend plea agreements with others facing similar firearms counts. The uncertainty is already changing the way prosecutors draw up and negotiate charges.