WASHINGTON — Tara Sheneva Williams’ last chance to leave her rural California prison alive may well have died Wednesday at the U.S. Supreme Court.

In a decision both technical and poignant, the court unanimously rejected Williams’ challenge to her 1993 murder conviction.

More broadly, the court’s decision Wednesday could affect the appellate prospects of Williams’ fellow inmates. And here, the consequences get complicated. While Williams definitely lost, her attorney said the Supreme Court’s opinion was a “well reasoned” one that avoids a far stricter rule proposed by the California attorney general’s office.

The reversal of an earlier appellate victory means Williams will remain incarcerated at the congested Central California Women’s Facility at Chowchilla, where she is serving life without the possibility of parole for her part in the slaying of a Long Beach, Calif., liquor store clerk named Hung Mun Kim. Williams was 20 at the time, and the driver, jurors concluded, of a getaway car in a robbery that went violently awry.

“For Ms. Williams, it’s a tragic day,” her attorney, Kurt David Hermansen, said in a telephone interview. “She’s depressed. It’s a stressful situation to get your hopes up, and then to have them crushed.”

A mother of two who has earned her associate’s degree while doing time, Williams’ personal hopes for eventually gaining her freedom may now rest with a future clemency request, or perhaps a long-shot appellate maneuver.

“It’s an uphill battle,” Hermansen acknowledged.

Williams appeared to have scored a victory in May 2011 when a three-judge panel of the 9th Circuit sided with her in concluding that her original trial judge had erred in replacing a holdout juror. The juror, according to the trial judge, was biased against the prosecution. But one day after this juror was replaced, the newly reconstituted jury found Williams guilty of first-degree murder.

Williams argued that the juror substitution violated her Sixth Amendment guarantees of a fair trial. The appellate panel agreed.

“A hung jury is never a desirable outcome in a criminal trial,” Appellate Judge Stephen Reinhardt wrote, but he added, “Unfortunately, the trial court cut some corners here.”

At the Supreme Court, though, the legal question turned away from what happened at Williams’ trial. Instead, justices framed her case as one testing when inmates have exhausted their opportunity to challenge their incarceration through a federal habeas corpus petition, the right of a person under arrest to appear before a judge.

While important, this question can seem arid even to legal professionals. On Wednesday, tellingly, Justice Samuel Alito spent barely a minute reading a brief summary of the decision that he wrote.

The limits on inmates’ legal challenges come under a 1996 federal law that lawmakers billed as a way to constrain frivolous prisoner litigation. Among other provisions, the law says prisoners can usually not seek habeas corpus relief in a federal court if a state court already has adjudicated the case on its merits.

A state court had rejected Williams’ claims but did not expressly say it was resolving her federal constitutional argument. The 9th Circuit concluded this meant the state court had “overlooked or disregarded” the constitutional issue, thereby enabling Williams to raise it anew in federal court.

The Supreme Court in its decision Wednesday said otherwise, noting that “it is by no means uncommon for a state court to address separately” federal claims.

In setting out the new rule, Alito said Wednesday that federal judges “must presume” that a state court that has rejected a federal claim has adjudicated it on the merits. In theory, this could rule out some prisoner petitions. At the same time, Alito and all of his fellow justices, except for Antonin Scalia, rejected California’s hard-line argument that would have made this presumption exempt from challenge.

Instead, the court is leaving prisoners a chance to rebut the presumption and thereby hold onto a legal lifeline.

“That approach,” Alito wrote, should “not prompt an unmanageable flood of litigation.”