For more than a decade, federal authorities painstakingly built a criminal case against the man they suspected of being the main drug supplier to the Hell's Angels of Minnesota. After spending untold hours on surveillance, cultivating informants inside the outlaw motorcycle gang, digging through garbage for clues and unraveling cryptic financial transactions, prosecutors this summer prepared to take the case to trial. Then, on the brink of proceedings in U.S. District Court in St. Paul, veteran IRS special agent Jim Shoup came forth with a stunning confession: He was tangled in a romance with the wife of the alleged drug...