After leading the nation for decades in recommending death sentences, juries in Dallas County and Harris County have apparently cooled to the idea. In Dallas, prosecutors have asked juries to condemn a murderer to death just two times since 2014, and in both cases the juries declined. That's good news for anyone concerned about how justice is meted out in Texas.

While there are crimes that probably deserve death, the defining characteristic of an execution is its irreversibility. Once carried out, there is no possibility for mistakes to be corrected. That's a problem for a criminal justice system whose mistakes are being brought to light more often than ever by advances in science and technology.

This basic incompatibility has helped soften support for the death penalty . (Other factors that may be playing a role: It is also expensive and has not been proven to be more a more effective deterrent against future crime than, say, the life sentence without parole that has, since 2005, been the minimum sentence for anyone convicted of capital murder in Texas.)

Dallas County District Attorney Faith Johnson has sought the death penalty in only two cases since taking office, which we hope suggests an increasingly high bar for executions in general. The first of them, however, was upended last week when new information about defendant Antonio Cochran's intellectual disability made him ineligible for execution, thanks to the Supreme Court's narrowing interpretation of when the Constitution permits the death penalty.

But it's a case out of Bell County not even involving a capital crime that best explains why our system of justice is fundamentally incompatible with the death penalty.

When jurors convicted George Powell of a Killeen robbery in 2009, it looked solid enough. A camera recorded the robber leaving the 7-Eleven, where he had put a handgun on the counter and told the terrified cashier to give him the cash and some cigarettes. The cashier told police the robber had been about 5-foot-6, according to a story published last week by Brandi Grissom, The Morning News' Austin bureau chief, but the clerk and a manager later testified that Powell, who is 6-foot-3, was the robber.

Eyewitness testimony has a lousy track record. And in this case, it was disputed by the manager of another store that had been robbed 12 days before — it was thought by the same robber — when she testified that she recognized Powell and he was definitely not the one who robbed her.

But prosecutors pointed to the video. And introduced an informant who told jurors that Powell had confessed while they were in jail.

Now, however, both the video and the snitch's testimony have been contradicted. The inmate says he lied to curry favor in his own case. And the video? An expert hired by the Texas Forensic Science Commission has concluded it is impossible that the man in the video was taller than 5-foot-9.

Powell remains in jail serving 28 years. An appeals court will have to decide whether all this means he's innocent. Lawmakers ought to ponder whether new standards for analysis of video evidence are needed, as the commission has suggested.

But whatever happens, we know that since he's still alive any mistakes in Powell's case can still be corrected. That's not possible for those who've been executed.

That's precisely why the death penalty remains fundamentally incompatible with justice.

Video evidence

Texas Forensic Science Commission recommendations regarding use of video evidence:

1. The basis for analytical conclusions reached in forensic casework must be supported by clear and comprehensive scientific methods.

Analysts should address error rates and uncertainty in their reports.

All analytical reports should be subject to peer review before use in a trial.

When post-conviction analysis is performed, the results should be immediately communicated to the prosecutor, the court and the defendant.

Analysts should follow established industry guidelines that are the consensus of the scientific community.

Analysts should take precautions to protect against confirmation bias.

In light of ... the concerns highlighted in this particular case, the commission's advisory committee should consider whether new licensing requirements for forensic analysts should be added.

The Bell County prosecutor should consider seeking further assistance from the FBI or another qualified law-enforcement forensic service provider if questions remain in the Powell case.

The criminal justice community should seek assistance and training when they encounter a forensic video analysis case and need to retain an expert witness.