A former high-ranking lawyer at the Federal Deposit Insurance Corporation pleaded guilty Tuesday in federal court to conspiring to sexually exploit multiple children and now faces a mandatory minimum prison sentence of 15 years. The lawyer, Mark Black, also previously served as president of the board of the Arlington Aquatic Club, a renowned Virginia swim club that includes U.S. Olympic swimmers among its alumni. Black resides in Arlington. Black, 50, most recently was special counsel in the general counsel's office of the FDIC, which insures the deposits of U.S. commercial and savings banks, according to his LinkedIn page. He has worked in the legal division since April 2013, his LinkedIn page says. The Department of Justice said Black, who is married and has teenage sons, was a member of "two o