The Morgan Stanley broker who was with Anna Gristina when she was arrested on charges that she ran a brothel on the Upper East Side of Manhattan, has been identified.  Hopefully he now will be able to capitalize on his new-found celebrity status - perhaps by closing on some leads and building up his book of business. David Spencer Walker was with Ms. Gristina at the time of her arrest - not far from one of Morgan Stanley’s offices in Midtown Manhattan.  Contrast that to the location of the brothel she allegedly operates out of an uptown apartment on East 78th Street. Mr. Walker was not taken into custody, according to people briefed on the matter but not authorized to speak on the record.  Court documents apparently indicate that, prior to her arrest, Ms. Gristina had been meeting with a Morgan Stanley employee to discuss Ms. Gristina seeking to secure financing for a new business.  The business was a proposed online dating service, according to a lawyer for Ms. Gristina. “She was endeavoring to get into a Web site that would have rivaled Match.com,” the lawyer, Peter Gleason, told reporters on Tuesday.  Mr. Walker did not immediately return a call left for him at his office.  Nor did he immediately notify his employer of his involvement in the case, according to the people briefed on the matter.  Senior staff at Morgan Stanley did not know his identity on Tuesday, despite the media attention surrounding the case. Who is This Broker? Mr. Walker, who has not been charged in connection with the investigation into Ms. Gristina, has a long history on Wall Street, according to information about him filed with regulators. Early in his career, he had spent time at both Bear Stearns and Lehman Brothers.  In the late 1990s, he worked at Merrill Lynch & Company before moving to Morgan Stanley in July 1999. In 2005, he jumped shipped for Citigroup, but ended up back at Morgan Stanley as the result of a merger.  Regulatory records show he has been involved in at least one customer dispute.  The case, in which a customer alleged mismanagement of her account in 2004, was denied.  Mr. Walker’s identity was reported earlier by Charles Gasparino on the Fox Business Network.    [Dealbook, 3/7/12]