I heard that for those cases capital punishment was supported by the people and that despite the Party wanting to eventually abolish it there were cases where they'd be disregarding public opinion which they don't do for democracy reasons

Also when someone is massively powerful, with big money and network, I wonder if it's really possible to actually keep them in prison. If you don't put them in inhumane conditions they might be able to keep doing corruption and sabotage from the inside, just like mafia lords often keep leading operations from their cells (and a US puppet is way more dangerous than a mafia lord to a country)