PHOENIX (AP) -- The man who pleaded guilty in the Arizona mass shooting that wounded former U.S. Rep. Gabrielle Giffords has returned to the Missouri federal prison where he is being treated for a mental illness.

U.S. Marshals Service spokesman Chris DeRosa says Jared Lee Loughner left Tucson on Friday and is at the U.S. Medical Center for Federal Prisoners in Springfield, Mo.

DeRosa says he will remain there until his sentencing Nov. 15.

Loughner was in Tucson this week for a hearing in which a judge allowed him to plead guilty to 19 counts stemming from the shooting. The plea agreement guarantees he will spend the rest of his life in prison.

Six people died and 13 others, including the congresswoman, were wounded in the Jan. 8 shooting outside a Tucson supermarket.