Truth in Trials Act - Amends the federal criminal code to: (1) allow any person on trial for a federal marijuana-related offense to introduce evidence that the alleged marijuana-related activities were performed in compliance with state law regarding the medical use of marijuana, (2) allow an affirmative defense to a marijuana prosecution that the alleged marijuana-related activities complied with state law regarding the medical use of marijuana, (3) limit the criminal liability of persons convicted of federal marijuana-related offenses, (4) require the preservation and return (if a defendant is acquitted) of property seized in connection with a marijuana prosecution, and (5) prohibit the seizure of plants grown or stored under a physician's recommendation or by order of a state or municipal agency in accordance with state law regarding the medical use of marijuana.