Two Texas death cases made headlines last week; both involved a parent who was convicted of killing their 2-year old child. Beyond this strange coincidence, the cases remind us that miscarriages of justice regularly occur in capital cases and also that revelations of such things are often not enough to stop executions.

In the first of those cases, a trial judge determined that Melissa Lucio, one of the few women on death row in the United States, is, despite her 2008 conviction of murder in the death of her 2-year-old daughter, “actually innocent.” But Lucio’s ordeal is far from over. The trial judge’s decision must be reviewed by the notoriously pro-death-penalty Texas Court of Criminal Appeals.

One day after the Lucio judgment was announced, the Texas Supreme Court cleared the way for the execution of Robert Roberson. Roberson was convicted in 2002 of killing his 2-year-old daughter “in a case that relied on evidence of shaken baby syndrome.”

Since then, that kind of evidence has been discredited and is now inadmissible in several states, including Texas. Moreover, it seems likely that the death of his daughter was an accident and not a crime at all.

Americans might think that evidence of innocence would be enough to get someone released from prison or death row. But unfortunately that is not the case anywhere, especially in Texas.

Whether in Texas or elsewhere, one might ask why evidence of innocence is not always enough to save someone’s life. First, no matter how powerful and persuasive, such evidence is not necessarily proof of innocence. At the end of the day, doubt may remain.

As law professor Lee Loevinger explained almost 50 years ago: “Neither judges nor juries, nor even lawyers in the usual situation, ever come in contact with the ‘facts’ of any case,........

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