presumption of the purchase of a thing
With regard to the presumption of the purchase of a thing manifestly not produced by the possessor, there is a 'rational connection between the fact proved and the ultimate fact presumed' (Luria v. United States, 231 U.S. 9, 25, 34 S. Ct. 10; Yee Hem v. United States, 268 U.S. 178, 183, 45 S. Ct. 470). Furthermore there are presumptions that are not evidence in a proper sense but simply regulations of the burden of proof. Greer v. United States, 245 U.S. 559, 38 S. Ct. 209. The statute here talks of prima facie evidence, but it means only that the burden shall be upon the party found in possession to explain and justify it when accused of the crime that the statute creates. 4 Wigmore, Evidence, 2494. It is consistent with all the constitutional protections of accused men to throw on them the burden of proving facts peculiarly within their knowledge and hidden from discovery by the Government. 4 Wigmore, Evidence, 2486.
CASEY v. U.S., 276 U.S. 413 (1928)