The United States government (plaintiff) prosecuted Erick Arias Campos (defendant) for illegal possession with intent to distribute of methamphetamine. At Campos's trial in the federal district court for the Northern District of Iowa, the government introduced police-officer testimony that they searched a multi-resident house, and although they found no drugs in any other residents' rooms, the officers found a distribution amount of methamphetamine in Campos's room, along with tools of the drug dealer's trade such as false identification papers, a gun, and ammunition. The officers also found a pen casing that contained methamphetamine residue. Campos testified that he had a large methamphetamine supply on hand only because he was able to get it at a bargain price, that he was a drug addict who intended to keep the whole supply for his personal use, and that he used the pen casing to ingest methamphetamine. Another defense witness testified that he saw Campos line up small doses of the drug in a typical arrangement for ingestion, though he never actually saw Campos ingest methamphetamine. The jury convicted Campos, who moved for a new trial.