On Tuesday, Mr. Epstein was moved to a suicide-watch unit at the detention center where he is being held, after officers found him unconscious in his cell with marks on his neck, according to people familiar with the matter. His July 6 arrest came amid criticism of a 2007 nonprosecution agreement with federal prosecutors in Florida, which he signed to resolve an investigation into similar allegations. As part of that deal, Mr. Epstein pleaded guilty in 2008 to state prostitution counts and spent much of his 13-month sentence outside prison due to work-release privileges. In a court filing after his arrest this month, Mr. Epstein listed assets worth more than $550 million, an accounting a federal prosecutor said in court "is more significant for what it does not include than what it does." Mr. Epstein listed no debts, and no art; he gave no indication of foreign accounts. People who have known or worked with Mr. Epstein over the past four decades say the figure likely doesn't represent the full picture of his fortune. While he may have made money from overseas investments or other endeavors, the bulk of his wealth appears to have come from a small number of very wealthy clients. Lawyers for Mr. Epstein didn't respond to requests for comment. Early in his career, Mr. Epstein forged profitable relationships, often by charming powerful people. As a math teacher at Manhattan's elite Dalton School, he so impressed the father of one student that the father urged a friend—Bear Stearns Cos. Chief Executive Alan "Ace" Greenberg—to hire Mr. Epstein. Mr. Greenberg did so in 1976. At Bear Stearns, Mr. Epstein worked for Michael Tennenbaum, a senior executive, selling the firm's analyses of stock options to clients. Soon, Mr. Tennenbaum learned that Mr. Epstein had padded his resume, falsely claiming to have graduated from Stanford University, Mr. Tennenbaum said in an interview and in a forthcoming memoir. Mr. Epstein confessed, telling Mr. Tennenbaum he h