61 L.Ed.2d 560 (1979); United States v. Zimmerman, 943 F.2d 1204, 1208-09 (10th Cir.1991). We will not uphold a conspiracy conviction obtained, however, by nothing more than “piling inference upon inference.” United States v. Fox, 902 F.2d 1508, 1513 (10th Cir.1990) (citations omitted). Under 18 U.S.C. § 371, a conviction for conspiracy requires that the government prove beyond a reasonable doubt that the defendants agreed to defraud the United States and that one of the conspirators committed an overt act in furtherance of the conspiracy. United States v. Guadalupe, 979 F.2d 790, 793 (10th Cir.1992). An agreement between the defendants to violate the law is an essential element, which must be shown beyond a reasonable doubt. United States v. Davis, 965 F.2d 804, 814 (10th Cir.1992) (<HOLDING>). See also United States v. Butler, 494 F.2d
holding various actions of state insurance commissioner insufficient evidence of agreement to bribe a public official holding that where a public official takes discretionary action that the official knows will directly benefit a financial interest that the official has concealed in violation of a state criminal law that official has deprived the public of his honest services under  1346 holding police officer is a public official holding state of north carolina and state official sued in their official capacity are immune from  1983 and  1985 actions in federal court holding local commissioner not liable to licensee for official act in revoking license