A former FBI agent key to special counsel Robert Mueller’s investigation into Russian meddling in the 2016 presidential election is one of several forensic accountants working on the Manhattan district attorney’s investigation into the Trump Organization, people familiar with the matter say.A former FBI agent key to special counsel Robert Mueller’s investigation into Russian meddling in the 2016 presidential election is one of several forensic accountants working on the Manhattan district attorney’s investigation into the Trump Organization, people familiar with the matter say.