Violent employee claims, 'It's because of my disability'

The situation: One employee “goes off” on another, and maybe even gets physically abusive or engages in harassment. You call in the offender, and he says, “I have a documented mental disability that causes me to behave that way.”And sure enough, the employee is telling the truth. What are your options? Do you have to “accommodate” the behavior?
To every HR manager’s relief, the short answer is no. You don’t have to excuse or accept abusive behavior even employees have valid mental or emotional disabilities, such as a psychiatric condition that lead to such behavior.
What EEOC says
Let’s look at what the Equal Employment Opportunity Commission says in its own handbook about accommodating violence or abusive behavior:
An employer never has to excuse a violation of a uniformly applied conduct rule that is job-related and consistent with business necessity. This means, for example, that an employer never has to tolerate or excuse violence, threats of violence, stealing, or destruction of property. An employer may discipline an employee with a disability for engaging in such misconduct if it would impose the same discipline on an employee without a disability.
In other words, as long as you’re consistent about how you discipline all employees for violent or abusive behavior, you’re probably in the clear. So, for instance, if your policy is to terminate after a first offense of violence, you can terminate immediately someone who engages in violence and then claims an emotional disability.
However, be aware that the law isn’t so clearcut when it comes to other types of offenses that don’t appear to pose a safety threat to your workers. For instance, if an employee is chronically late to work because of an emotional disability, you may have accommodate the tardiness if being on time is not absolutely crucial to getting the job done.
 You can take a look at the EEOC’s Enforcement Guidance on Reasonable Accommodation and Undue Hardship Under the Americans with Disabilities Act by going to: http://www.eeoc.gov/policy/docs/accommodation.html