Galen Marsh, 30, took data on about 10 percent of Morgan Stanley’s 3.5 million wealth management customers, the bank says. The Federal Bureau of Investigation is investigating the leak, a source says. Mr. Marsh, who had been with Morgan Stanley since 2008, was quickly fired and is the subject of a criminal investigation by the FBI. The case could be damaging for Morgan Stanley because the firm has become increasingly reliant on the success of its wealth management division as it has de-emphasized riskier trading.”]