Death penalty in S.H.E.I.L.D.

So I am watching ultimate spiderman season 3 episode 3. doctor octopus is imprisoned once again after he made venom to heighten alien strength and ability to take over the world with Loki at his side. They had an army and the avengers demolished new York city all over the place mainly in midtown trying to defeat the enemy. The army and Loki were thrown in a desert plain in another universe as imprisonment and Doc Oct is placed in , given one of the highest level of security there is, in the helicarrier of all places. My question is if we today enforce death penalty why hasn't S.H.E.I.L.D. enforced this, don't they have judgement system? It's not central to U.S. since we all know they do world wide missions seen mostly for U.S. , so I'm guessing United Nations works with them or they work under them, I'm not sure (anyone?) but nearly every government enforces it and always has at one point so I would say they would OK the death of a highly dangerous criminal. Does anyone have any insight on this too? I believe that it is because it would become a manga type plot where it has a near finish and a a bit irrelevant to an everyday life, hence Marvel and DC. (does that make sense?)