Good question. Davis was indicted for treason. Eager to argue his case, Davis demanded to be put on trial without delay. But the government botched the case and eventually dropped the charges, and Davis went on to become a celebrity on both sides of the Potomac.
Botched? On purpose maybe. To put Davis on trial would mean putting the legality of secession on trial. Since secession in not unconstitutional and congress has passed no laws against it, Davis would have won. Couldn't have that...