FastCase Premium is the component of HeinOnline that provides full-text access to the current and historical, civil and criminal, State and Federal case law of the United States. HeinOnline's library guide has a detailed description of FastCase Premium.
This link takes you to an excellent video about How to Search Case Law
As a supplement, HeinOnline’s U.S. Supreme Court Library includes the U.S. Reports, which contain the officially-published opinions of the U.S. Supreme Court and are available from inception to current.