I do not know why the Amtrak train derailed, how could I possibly make a claim?

While overall Maryland and the District of Columbia have very safe transportation systems the sheer number of people using them and the nature of the buses and trains utilized results in catastrophic injuries on a fairly routine basis.
Train derailments while infrequent cause many injuries.  As a consequence, detailed investigations are performed of such things by the appropriate governmental authorities.  Accessing this information and participating in the investigation can be a valuable tool in assisting your attorney in developing your claim.