When Harry Markopolos dropped his bombshell report skewering General Electric Co., he revealed that he was working with a short seller to profit from the stock’s decline. More than a week later, that firm’s identity remains a mystery. Markopolos has offered few details about his partner, saying only that it’s a midsize hedge fund based on the East Coast -- and one not normally known for shorting. “I promised confidentiality,” the accounting examiner said on CNBC. Off-the-record conversations with a number of players in the short-seller community haven’t turned up much intel either.