Velasco-Heredia

This case requires us to assess once again the effect of Apprendi v. New Jersey, 530 U.S. 466, 488 , 120 S.Ct. 2348, 2362-63 , 147 L.Ed.2d 435 (2000) on the federal drug statutes. 21 U.S.C. § 841 et seq. (West 2000). Specifically, we must consider whether the district judge erred by employing the preponderance of evidence standard of proof to determine the amount of marijuana attributable to Defendant-Appellant Arturo Velasco-Here-dia (“Velasco-Heredia”), and, if the judge did err, whether the error was harmless.

We have jurisdiction over this timely appeal pursuant to 28 U.S.C. § 1291 , and for the reasons explained below, we vacate Velaseo-Heredia’s sentence and remand the case to the district court for further proceedings.

I

Background

A. Factual History

During the last few weeks of May, 1999, the United States Customs Service (“Customs”) conducted surveillance of a suspected marijuana “stash house” at 614 Alice Street in San Diego, California. One of the vehicles spotted at the 614 Alice Street home was a Mitsubishi pickup truck registered to Arturo Velasco-Heredia. On June 4, 1999, Velasco-Heredia drove this pickup from Mexico into the United States at the San Ysidro,…