Robert Roberson expected to testify in person before Texas House ...

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Over six hours on the day Robert Roberson was set to be put to death, Texas House lawmakers waged a rollercoaster legal battle to delay his execution, setting off a separation-of-powers conflict that would have to be resolved before the state could resume its execution plan.

The Texas Supreme Court halted Roberson’s execution late Thursday — the first time in Texas history, experts believed, that one high court blocked an execution that was already approved by the other. The Texas Court of Criminal Appeals repeatedly declined to stop Roberson’s execution, clearing the way for it to move forward earlier that same day.

The Texas Supreme Court’s order came as a result of a Hail Mary subpoena a Texas House committee issued to Roberson in a frenzied bid to save his life. The lawmakers, who warned the state was about to kill a likely innocent man, got their way — at least for now.

Roberson was convicted in 2003 in the death of his chronically ill 2-year-old daughter Nikki, who was given a shaken baby syndrome diagnosis that many experts and lawmakers say is no longer supported by the scientific evidence. Roberson has maintained his innocence over two decades on death row, while prosecutors say evidence of abuse is still convincing.

Roberson is still sentenced to die. He is expected to testify before the Texas House panel that subpoenaed him on Monday.

Here’s what you need to know.

The subpoena

The Texas House Committee on Criminal Jurisprudence voted unanimously on Wednesday to subpoena Roberson, directing him to testify before the panel at an Oct. 21 hearing — four days after his scheduled execution.

On Thursday, hours before Roberson was set to die, state lawmakers asked the court for a stay of execution to allow him to respond to the subpoena.

They argued that only Roberson could provide unique testimony relevant to the committee’s work on criminal justice matters, and in particular, the state’s pioneering 2013 junk science law — which Roberson had tried, and failed, to use to prove his innocence.

“His testimony on his access to justice and due process are unique because he is a person with autism in a case unlike any other in the State of Texas — the first potential ‘shaken baby syndrome’ execution,” state Reps. Joe Moody, D-El Paso, and Jeff Leach, R-Plano, wrote to the Texas Supreme Court. “No other person can provide the Committee with this information. Given the dispute over some of the facts surrounding his case, it is also essential for the Committee to hear from him personally to judge his credibility as a witness.”

All of Roberson’s appeals have been rejected by the courts so far, raising concerns among lawmakers that the courts were failing to properly implement the state’s junk science law. That law was created to allow the courts to overturn a conviction if the science at the center of the case had since changed or been discredited.

Roberson is expected to appear in person for testimony before the Texas House criminal jurisprudence panel on Monday, in response to the committee’s subpoena.

The Texas Supreme Court’s order

The Texas House committee’s subpoena triggered a separation of powers issue that the Texas Supreme Court ordered a lower court — the Travis County District Court — to resolve before Roberson’s execution date could be reset.

The legislative subpoena of a condemned man — a novel legal maneuver — created conflicting legal obligations for the Texas Department of Criminal Justice, an executive branch agency: either execute Roberson on Oct. 17 as scheduled, or produce him for testimony on Oct. 21.

That bind raised the constitutional question of which branch’s authority — the legislative or the executive — reigned in a scenario of competing legal directives.

“Whether the legislature may use its authority to compel the attendance of witnesses to block the executive branch’s authority to enforce a sentence of death is a question of Texas civil law, not its criminal law,” Texas Supreme Court Justice Evan Young wrote in a concurring opinion Thursday. “The question implicates the distribution of authority among the three branches of government, pitting two branches against each other. ... These questions implicate the separation of powers at a high level.”

The legal maneuvering began when House lawmakers got a Travis County judge to issue a temporary restraining order blocking Roberson’s execution. In turn, the Texas Court of Criminal Appeals vacated the order on Attorney General Ken Paxton’s request, which prompted state lawmakers to ask the state supreme court to intervene, and the execution was blocked again.

The restraining order is valid through Oct. 31, when the Travis County district court judge will hold a hearing on Texas lawmakers’ application for an injunction pending a full trial on the merits of the separation-of-powers issue.

Where does this all leave Roberson?

It remains to be seen how long it might take the court to resolve the separation-of-powers conflict, meaning it’s unclear how long Roberson’s execution could be delayed.

The prosecutor in Roberson’s case must also request a new execution date, which cannot be within 90 days of when the state requests a new date.

Gov. Greg Abbott could also grant a one-time, 30 day reprieve. He has so far remained publicly silent on the case.

And as remarkable as the Texas Supreme Court’s stay was, Roberson is still sentenced to death. And the high court was clear in its order that the outstanding discussion should focus tightly on the separation-of-powers question — without delving at all into Roberson’s case.

“This Court has no authority over criminal sentences, but the Court of Criminal Appeals does, and that court has repeatedly considered this case,” Young wrote in his concurring opinion. “Anything other than laser-like focus on the specific civil-law questions presented — and especially the competing authority of the legislative and executive branches in this situation — is therefore off limits.”

It’s unclear what remaining legal recourse Roberson has. The U.S. Supreme Court, the state’s highest criminal court and his trial court have all declined to vacate his execution and grant him a new trial over several rounds of appeals. The state’s parole board voted unanimously on Oct. 16 to recommend against granting clemency.

But there are situational factors that could change over the course of Roberson’s stay, with ramifications for his case.

Three of the five judges on the Court of Criminal Appeals who voted to allow Roberson’s execution to proceed are set to leave the bench at the end of the year after Paxton-backed primary challengers unseated them. If even one of the incoming judges elected in November takes a different view of his case, it could shift the landscape in Roberson’s favor. But a conservative sweep on a court that has already repeatedly rejected Roberson’s appeals could diminish his already long-shot chances.

The Legislature will also come into session in January. Members of the Texas House, at least, have indicated they could consider amendments to the 2013 junk science law, with potential consequences for Roberson’s appeals. Whether any amendments could become law, on the other hand, is unclear, as is whether Roberson’s stay might extend long enough to see statutory change.