It is to be ascertained that why this particular employee has been targeted while other employees in the same organisation did not have any grievances in their work spot.
If a customer assaulted the employee in the work spot, nothing prevented the employee to report this incident to the top brass of the company if he did not get any response or support from the immediate boss.
If there was no response from the top management too, then he could have approached police with a complaint agaisnt the assaulter.
If the employee was demanded money for making his performance rating better, it is nothing but asking bribe, the employee had opportunities to expose the corrupt official to the management.
Above all, if the employee was not able to tolerate the work atmosphere, he could have taken transfer to some other place of the same company, if there are no other branch elsewhere, he can very well look for a better employment elsewhere by quitting this job.
It will not be possible to initiate any legal action for the trivial things because most of them do not have evidence, hence no case will be maintainable.
It is always better to have some cooperation and flexible situation in the working atmosphere so that such things can be avoided or ignored.