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The court blocked Thursday's execution of Thomas Arthur

Chief Justice John Roberts joined four other justices, in a courtesy move

(CNN) —  

Here’s how much Chief Justice John Roberts cares these days that his branch of government functions as a collegial body.

Around midnight Thursday, the conservative justice cast the deciding vote to put the pending execution of Thomas D. Arthur on hold. In an unusual statement, he said he acted not because he thought the inmate’s last minute plea merited the court’s review.

The move comes as the court continues with only eight justices since February’s death of Justice Antonin Scalia. With four conservative-leaning justices and four liberals.

“I do not believe that this application meets our ordinary criteria for a stay,” Roberts wrote. Instead, he said, he stepped in because four of his colleagues voted to grant a stay.

While it takes only four justices to agree to take up a case, it takes five to stay an execution.

“To afford them the opportunity to more fully consider the suitability of this case for review,” Roberts wrote, “I vote to grant the stay as a courtesy.”

Granting a so-called “courtesy vote” is not a novel concept, says expert Eric M. Freedman of Hofstra Law School. During the 1980s the court did so routinely in capital cases.

But in the recent past, the court has allowed executions to go forward, even though four justices wanted to grant the stay.

“Chief Justice John Roberts did the right thing last night, ” said Freedman, the author of a Law Review article on the subject.

“In giving the Court the time to consider fully a case where life is at stake, all those concerned about the court’s decision making process hopes the practice continues once the court is back to full strength,” he said.

Arthur’s case concerned Alabama’s lethal injection protocol, an issue that has deeply divided the justices in the past in other cases. He was convicted for the 1982 contract killing of Troy Wicker.

“I am inclined to guess the Chief thought it particularly useful to showcase this particular kind of collegiality at this particular moment,”said Douglas A. Berman of the Ohio State University Moritz College of Law.