IDAHO FALLS — Never mind that he was a multimillionaire. Daren Palmer was quick to carry furniture when someone in his congregation was moving. He volunteered at the church farm. He got down on his knees to clean the sanctuary.

“I saw him do it,” said Penny Peterson, a family friend.

Mr. Palmer was also the picture of success, a humble hometown investor with seemingly flawless instincts who promised returns of up to 20 percent for his clients, many of whom he worshiped with or whose sons he coached in football. In this conservative city, frequently atop best-places-to-live lists for its blend of ambition, livability and quiet mountain beauty, he traded in trust.

When he decided to build his family’s dream house, a 16,000-square-foot structure with an elevator, a pool house, an enclosed basketball court and a heated travertine staircase, he did not seek a reclusive estate on the Snake River. He chose a subdivision lot directly across the street from where he spent Sunday mornings, the Church of Jesus Christ of Latter-day Saints.

“Work hard, take care of yourself, take care of your family, that’s one of the things the church says to do,” Ms. Peterson said. “Bernie Madoff, I’m sure he wasn’t out cleaning churches.”