Reposting my comment above - you only need the OP’s words and some reasonable logic to arrive at that conclusion:

        These people tell me HR knows it but everyone is afraid of getting sued or something so it's a don't ask don't tell situation. People simply ignored him.
    
    This doesn’t require soft skills to logic out that there is reasonable trouble.
    
    Coworkers, with a preexisting work history with this employee, know that HR is afraid of getting sued.
    
    Why would an HR department be afraid of being sued by an employee?
    
    The most likely explanation is that they want to fire them for performance and are trying to limit the likelihood of a lawsuit.
    
    Why would a coworker be able to speak to HR’s internal assessment of an employee’s ability to be fired?
    
    The most likely explanation is that they’ve gone to HR, or a manager, with problems, and the manager has asked HR if they could fire the employee for cause before.
    
    “People simply ignored him” is more ambiguous, but in the context above, I take it to mean - other coworkers want him fired, but given HR’s inaction, they are taking their own action by ignoring the coworker and working around them rather than trying to include them.