He is currently held in the Supermax Prison in Florence, Colorado. He had the Unabomber, Terry Nichols, and Timothy McVeigh as his cellmates.
Another one in the Supermax is Ramsi Yousef. But I do remember Langan testifying (or wanting to testify) at Terry Nichols' state trial this year.
Well, by November 2001 Timothy McVeigh had been executed, so it wasn't McVeigh.