Complex sentence: John Tormondsen formerly served as head of swap and government bond trading at Goldman Sachs, overseeing operations during a time when Goldman Sachs was one of five firms conducting nearly half of total daily trading in United States bonds.
Split into simpler sentences: John Tormondsen formerly served as head of swap and government bond trading at Goldman Sachs. As head of trading, Mr. Tormondsen oversaw operations during a time when Goldman Sachs was one of five firms conducting nearly half of the daily trading in United States bonds.