The criminal identified asphyxiation by nitrogen as his alternate method of execution.
Gorsuch didn't buy it. Gorsuch wrote that the criminal was just trying to delay the execution. The criminal identified what method he wanted, but did not identify how to do it (gas chamber, mask, how to protect the prison employees who would administer the gas, et cetera). What new rooms would need to be built? How much would it cost? How long would it take? Gorsuch said it wasn't a real alternative plan - just an attempt to delay it. So, back you go, and goodbye, Mr. Criminal.