A federal jury found former Goldman Sachs Group Inc. GS +2.11% trader Fabrice Tourre liable for misleading investors in a mortgage-linked deal that collapsed during the financial crisis, delivering a historic win for a U.S. regulator eager to prove its mettle inside the courtroom. The panel of nine jurors reached their verdict during the second day of deliberations, finding Mr. Tourre liable on six of seven claims that he violated federal securities law. "It was a long, slow process," said juror Beth Glover, a 47-year-old Episcopal priest, after the verdict. The victory is an important one for the Securities and...