Story highlights The court blocked Thursday's execution of Thomas Arthur

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

Washington (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.

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