A St. Louis woman who served more than 16 years in prison for a murder she maintains she did not commit was released from prison yesterday after a federal judge overturned her conviction, calling the case Missouri prosecutors built against her "fundamentally unfair."

Ellen Reasonover walked out of prison a day after U.S. District Judge Jean C. Hamilton ordered authorities to release her. Missouri officials said they would not retry Reasonover.

"I'm free," Reasonover, 42, cried in a telephone interview as her attorneys drove her in a car from Chillicothe Correctional Center in Chillicothe, Mo., where she has been held since her 1983 conviction. "I'm so excited. I'm going home to see . . . my family. It's been a long time. I'm happy right now."

In Hamilton's ruling on Monday, which came after the judge heard new evidence in the case, Hamilton wrote that prosecutors had withheld from Reasonover's attorneys evidence that could have proven her innocence. "The prosecution's failure to turn over evidence favorable to the defense rendered [Reasonover's] trial fundamentally unfair and deprived [her] of her rights under the due process clause," Hamilton wrote in her 75-page ruling.

Reasonover was sentenced to 50 years in prison without the possibility of parole in December 1983, after a jury found her guilty of killing a 19-year-old gas station attendant during a robbery. She did not testify during the trial phase of her case. But at the sentencing phase, when the jury heard testimony about whether Reasonover should be executed or serve life in prison, she told the jurors she did not commit the crime. The jury was unable to agree on a sentence, and the judge decided her punishment.

She had been convicted of killing James Buckley, an attendant at a gas station in Dellwood, Mo., a suburb of St. Louis. No witnesses placed her at the scene. Police found no fingerprints and no murder weapon. Prosecutors said her motive was robbery, but no money was taken from the cash register and about $3,000 was left in an unlocked safe.

The Washington Post published a two-part series in June 1984 that uncovered new evidence in the case and raised serious questions about Reasonover's alleged jail-house confessions, which were the key weapons prosecutors used to gain a conviction.

The jury relied almost entirely on the testimony of two inmates, Rose Jolliff and Mary Ellen Lyner, both of whom testified that Reasonover confessed to them. The Post reported that both prisoners had long criminal records, histories of drug addiction, and benefited from their testimony--which prosecutors did not tell the jury. In addition, five other women, including three who were in the small cells with Reasonover when she allegedly made her confessions, told The Post that they never heard Reasonover say anything incriminating.

At the evidentiary hearing in June 1999, two tapes of conversations with Reasonover that police secretly had recorded further challenged the testimony of Lyner and Jolliff.

One of the tapes was a conversation between Reasonover and Jolliff, four days after Reasonover allegedly confessed to Jolliff in a jail cell. Reasonover had been released. At the request of police, Jolliff called Reasonover at home. During the conversation, Reasonover told Jolliff repeatedly that she was innocent of the crime.

That tape surfaced at the June 1999 hearing. The prosecutor in the Reasonover murder trial, Steven Goldman, who is now a St. Louis County judge, testified at the evidentiary hearing that he never heard nor saw the tape before.

In her ruling, Hamilton wrote that "had the tape been disclosed . . . it would have . . . had a devastating impact on Jolliff's credibility at trial."

The second tape uncovered in 1996 by investigators for Reasonover's attorneys was of a conversation between Reasonover and her boyfriend, Stanley White, whom police had also questioned in the case. Police put Reasonover and White in jail cells next to each other and secretly taped their conversation in which they both repeatedly said they had no involvement in the murder.

Hamilton's ruling was reviewed yesterday by Missouri Attorney General Jay Nixon, who has decided not to appeal the decision, said Scott Holste, a spokesman for Nixon.

Her lawyers were notified of Nixon's decision late yesterday after visiting Reasonover earlier in the day. They quickly returned to the prison to have her released.

"It is a very strong and powerful decision, said Richard Sindel, one of Reasonover's attorneys. "Virtually every point that was raised . . . was found in our favor . . . The evidence that was presented by the prosecution was not credible and the evidence that would have been presented by the defense was."

"The court clearly brands the two star witnesses against Ellen as liars," said Jim McCloskey, founder and executive director of Centurion Ministries Inc., a nonprofit group that has been working to get Reasonover released since 1993, after her appeals in state courts had been exhausted. "This whole case was insane."