WASHINGTON — (CNN) Amid new scrutiny of American capital punishment practices, President Barack Obama said in an interview released Friday he was disturbed by the practical effects of the death penalty.

While Obama said he wasn’t opposed “in theory” to killing criminals convicted of heinous crimes, he said that data showing racial biases and wrongful convictions have prompted him to wonder whether the death penalty remains a legitimate tool.

Obama was speaking to former New York Times editor Bill Keller, who now runs The Marshall Project, a news organization focused on criminal justice issues.

“There are certain crimes that are so beyond the pale that I understand society’s need to express its outrage,” he said. “So I have not traditionally been opposed to the death penalty in theory. But in practice it’s deeply troubling.”

Saying he’s “struggled for quite some time” over the death penalty, Obama also said recent botched executions have led him to wonder whether the application of capital punishment is still legal.

“We know that in the application of the death penalty we’ve had recent cases, by any standard, it has not been swift and painless but rather gruesome and clumsy,” he said.

In the aftermath of one of those executions gone wrong — an Oklahoma incident that left an accused murderer writhing and convulsing for several minutes — Obama asked the Justice Department to conduct a review of death penalty practices.

Since then, several states have suspended executions, either for legal reasons or because drug companies have stopped supplying the drugs needed for lethal injections.

This week, conservative Supreme Court Justice Antonin Scalia said “it wouldn’t surprise me” if the high court strikes down capital punishment in the United States, he told CBS News, though he’s made similar predictions in the past.

But the case to abolish U.S. executions has gained greater traction in recent months, including an opinion from liberal Supreme Court Justice Stephen Breyer, who questioned the constitutionality of capital punishment in an opinion this summer.

“This is not what people expected when they wrote the cases upholding the death penalty more than forty years ago, and therefore I think it’s time to revisit the issue,” Breyer told CNN’s Wolf Blitzer in an interview this fall.

The-CNN-Wire ™ & © 2015 Cable News Network, Inc., a Time Warner Company. All rights reserved. (Photo: CNN)