As Texas prepares to execute it's 15th inmate of 2013 Tuesday evening, new polling data suggests support for the death penalty is on the decline.

A recent Gallop poll shows Americans' support for the death penalty is at its lowest level since 1972 -- just 60-percent -- due in large part to the growing number of exonerations.

“I think the innocence issue connects with broader awareness that our criminal justice system, like any other human institution, is imperfect,” says death penalty expert Douglas Berman from Ohio State University.

That growing number of exonerations however, makes the case to keep the death penalty.

“Every time we find out about an innocent person sent to death row we adjust our procedures, we heighten our concerns, we scrutinize our advocacy to make sure nobody innocent ever gets sent to death row,” he tells KTRH News. “The fact that we're doing that perhaps derives more support for continuing to use the death penalty.”

Berman says just like pro-abortion or legalization of marijuana, anti-death penalty advocates are making their voices heard across the country.  However, he says there will always be cases where capital punishment comes into play.

“The Colorado theater shooting or the Boston bombing are cases where most people believe the issue isn't guilt, the issue is only whether the death penalty is an appropriate punishment,” he says.

Tuesday's execution in Texas involves 49-year-old Jamie McCoskey, convicted in the 1991 kidnapping of a Houston couple in which he raped the woman and stabbed her boyfriend to death.