So, to cut a long story short. There's an employee I work with that has stolen money and property multiple times, and that has created a hostile environment for the rest of us via the use of intimidation and threats of violence. However, our HR have their hands tied regarding any form of further discipline due to our country's laws, and his threat of a lawsuit if he is ever fired. Some employees have decided to see if they can not provoke, more trick, him into losing his cool (he has a history of a foul temperament) and attack a colleague physically, ergo providing HR a credible excuse to finally fire him, and protect themselves at the same time. The main part of the plan is not to involve the cops, as we have no intention of causing unnecessary hassle, we just want rid of him. Would such an action be illegal under law?
In the United States, many jurisdictions have criminal offenses outlawing behavior that may include what you're describing here.
In Ohio, for instance, disorderly conduct (R.C. 2917.11) includes "insulting, taunting, or challenging another, under circumstances in which that conduct is likely to provoke a violent response."
In Indiana, there's the offense of provocation (IC 35-42-2-3), which is even broader and includes "recklessly, knowingly, or intentionally [engaging] in conduct that is likely to provoke a reasonable person to commit battery." It looks like this has been interpreted to include even actions that don't directly involve the provoked person, such as kissing another man's wife.
Beyond the criminal offense, there are also jurisdictions that will permit a civil suit for damages resulting from the criminal act. There are also states where this could constitute intentional interference with business relations or intentional interference with an employment contract. In any of those cases, your co-workers could be looking at damages for lost wages, loss of reputation, etc.