Employment Law Questions? Ask an Employment Lawyer.
They can be sued for "spoliation of evidence" (this isn't a great cause of action, but it is a potential one). You should be represented by a personal injury attorney for your assault claim, and they can assist you with the claim against your employer.
You may want to consider potentially joining your employer as a defendant in the suit against the assailant for an unsafe work environment (again, I hope that you have a personal injury attorney representing you, and you can explore whether or not this is a viable option to pursue in your specific circumstance).
If you do not currently have a lawyer representing you, you can find local plaintiff's lawyers (also called "trial attorneys") using the State and local Bar Association directories, or private directories such as www.AVVO.com; www.FindLaw.com; or www.Martindale.com (I personally find www.AVVO.com to be the most user friendly).