Four suspects remained at large Wednesday evening after arrest warrants were issued for 23 people, including 20 from Bulloch County, on federal tax fraud charges. The arrests followed a months-long investigation regarding fraudulent tax returns, the U.S. Attorney's Office for the Southern District of Georgia said in a news release. The roundup occurred after a federal grand jury in Savannah returned six indictments Tuesday charging 12 defendants with 115 violations of federal law involving fraudulent tax returns.