If they had been serious rather than play-acting, the leaders would have jumped at the chance to die for the "crime" of speaking truth to power.
Unless you're talking about secret assassinations carried out by traffic accident or similarly deniable means, months after the fact to prevent a PR problem, out of spite rather than to silence. I'm not sure what could be done about that sort of thing.
rm_-rf_slash is referring to plans by the FBI to shoot Occupy protestors "if the need arose" that were leaked after the main occupations were broken up. The NYPD for example set up an elaborate surveillance center and identified "leaders" in the movement for such a scenario. Other police units around the country did the same or similar.
Unless you're talking about secret assassinations carried out by traffic accident or similarly deniable means, months after the fact to prevent a PR problem, out of spite rather than to silence. I'm not sure what could be done about that sort of thing.