A Columbus man has confessed to the 2007 assault that left a Duncan man in a coma. Platte County authorities say Christopher Shea confessed during a polygraph exam that federal authorities gave to him. Randall Scott Michalak of Duncan was left in a coma, following the assault. He and 26-year-old Bryan Groene, were charged with first-degree assault in the Aug. 10 beating of Michalak outside a city bar. A jury will determine the credibility of the witnesses at trial. Shea also had his bond lowered to 10 percent of 25-thousand dollars.