The attorneys for the two men serving life sentences for the 1988 crime say the letter and new DNA evidence proves their innocence.
Critics of Texas Gov. George. W. Bush and the death penalty say the case is further evidence of flaws in the state's justice system. Texas leads the nation in executions.
The four-page letter by Achim Josef Marino, who is serving a life sentence for aggravated robbery with a deadly weapon in a separate case, was stamped "received" by the governor's office on Feb. 24, 1998, but was never forwarded to law enforcement officials.
In the letter, Marino claims he was responsible for raping and murdering a 20-year-old Austin woman in 1988, and that two men now doing time for the crime were innocent.
"I did this awful crime and I was alone," he wrote.
One of the two men convicted for the murder, Christopher Ochoa, claimed that police threatened him with the death penalty unless he confessed to the murder and testified against Richard Danziger.
Danziger maintained at trial that Ochoa and police were lying about his guilt. Both men were convicted.
Recent DNA testing now suggests that neither Ochoa nor Danziger was involved in the murder, and attorneys and prosecutors are re-examining the evidence in the case.
Danziger, 30, is eligible for parole in November 2003, and is currently held in the Skyview Psychiatric facility in Rusk, Texas. Ochoa's file was not available through the Texas Department of Criminal Justice.
A spokesman for the governor says Bush never saw the letter of confession and that such mail is usually forwarded to the appropriate law enforcement agency.
However in this case, the spokesman said, the letter was not forwarded because Marino wrote that he'd already confessed in a letter to the Austin police chief several years earlier.
"How can you be confident that you have a system in place that's going to adequately investigate these kinds of claims if this one could fall through the cracks so egregiously?" asks defense attorney Barry Scheck of the Innocence Project, a project that promotes DNA testing to assist inmates who claim innocence.
Asked about the case on the campaign trail, Bush said "Mr. Marino's case was fully looked at by the Austin Police Department."
But the state's criminal justice system has come under fire before.
Texas has executed 232 people since 1982 and 33 people so far this year. Seven more executions are scheduled for 2000. One-hundred-forty-five people have been put to death since Bush became governor.
Due to the sheer number of executions, death penalty opponents have raised the possibility that innocent people may have been placed on Texas' death row.
The concerns about Texas reflect a new scrutiny of death penalty convictions in general.
Illinois decided in January to declare a death penalty moratorium after DNA evidence spared 13 people on that state's death row from execution. Columbia University researchers reported in June that a study of nearly 5,800 capital cases from 1973 to 1995 found serious errors in 68 percent.
Bush, however, has always insisted that everyone executed in Texas was guilty, and said that he reviews each death penalty case personally.
In June, he said of the 145 put to death during his tenure, "I believe they've had full access to the courts and full access to have a fair trial, not only in the state system, but in the federal system."
That month, Bush stopped the scheduled execution of Ricky McGinn for DNA tests to confirm his guilt in the 1993 rape of his 12-year stepdaughter, whom he was also convicted of murdering.
Rape is an aggravating charge that can lead to the death penalty in Texas. Subsequent tests found McGinn was responsible, and he was executed in September.
Also in June, Bush decided not to intervene to stop the execution of Gary Graham, who was convicted in a 1981 murder on the testimony of a lone eyewitness, represented by a lawyer whose competence was questionable. Appeals courts and the state parole board alsrejected Graham's claims of innocence.
In a report scheduled for release Monday, the Texas Defender Service cites 84 capital cases in which a prosecutor or police "deliberately presented false or misleading testimonyconcealed exculpatory evidence or used notoriously unreliable evidence from a jailhouse snitch."
The next man due to die in Texas is 27-year-old Jeffrey Dillingham, convicted in the 1992 murder-for-hire killing of a Fort Worth couple. His execution has been set for Nov. 1.
In a statement Tuesday, Bush's presidential campaign said that crime has dropped dramatically during the governor's time in office, with the state reporting its lowest overall crime rate in 25 years, its lowest violent crime rate since 1985 and its lowest murder rate since the 1950s.