Ten Republican senators want Defense Secretary Ash Carter and Joint Chiefs Chairman Gen. Joseph Dunford to explain why a controversial detainee was released last month from the military prison at Guantanamo Bay, Cuba.

The letter sent Friday expressed concern over whether proper procedures were followed in the Oct. 30 release of Shaker Aamer, a Saudi citizen and British resident.

"Upon reviewing the notification of transfer, we noticed that the Joint Chiefs of Staff was not one of the entities listed as 'concurring' and 'approving' of the transfer, as is the norm," the senators, led by Tom Cotton of Arkansas, wrote. Their letters asked Carter and Dunford to provide details of why the Joint Chiefs did not approve of Aamer's release.

Republicans Pat Roberts and Jerry Moran of Kansas, John Boozman of Arkansas, Ron Johnson of Wisconsin, Marco Rubio of Florida, Thom Tillis and Richard Burr of North Carolina, Rob Portman of Ohio and Susan Collins of Maine also signed the letter.

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