The Superior Court abused its discretion in rejecting the defendant's insanity defense where the defendant substantially complied with the notice requirements of Rule 12.2(a) of the Federal Rules of Criminal Procedure and the Government had actual notice of the defense approximately five weeks before trial. Because the defendant presented evidence establishing that he committed the charged criminal acts in consequence of his mental illness, and the Government failed to meet its burden of rebutting that evidence, the Court reversed the defendant's conviction.