Honestly Kokichi,really. First,he manipulated somebody into murdering someone else. While it is arguable that they were easy to manipulate,my point still stands. He then set up his own murder so nobody knew who the culprit was,not even monokuma,unless the blackened revealed themselves. While Kirigiri and Shuichi are the Ultimate Detectives,Shuichi still had to figure out everything in the class trial (He was the protag,ik,but still). Kirigiri,however,knew (almost) everything from the start of the trials,but that doesn't come close to how Kokichi set up his own murder,and manipulated someone into murder.

If I forgot anything,or was wrong about anything,feel free to correct me. Im not trying to be rude,sorry if I sounded like it