Normal legal proceedings would involve having the accused in custody, a police investigation is conducted, and the case is brought to trial where prosecution and defense attorneys may take all the time to prove their points. Only if the accused is found guilty would he be sentenced. Only if capital punishment is permitted can such a sentence be carried out and only after a round or more of appeals.
In an extra-normal situation, a normal police investigation cannot be carried out - intelligence services (spys) must be employed - and a sentence of "guilty as charged" equates to capital punishment. It's not optimal, but if the accused poses a large enough threat, an abbreviated or extra-normal judicial system must be employed.