This puzzle isn't really possible to solve on the internet, so all I can do is describe it.
When teams arrived at the Main Quad, they found the following message from Mr. Boddy chalked around the rose in the center of the quad in blue chalk:
I have entrusted the final clue to one of my closest confidants. However, as he fears for his safety, he will only use a form of long distance communication that can’t be tracked electronically. He has encoded his location somewhere in this Quad, you’ll need to know the form of communication to find him. Once you find him, ask him “WHODUNIT.” Good luck. –Boddy
and they found an arrow labeled "UP" pointing towards The Oval. They also found that seven of the eight planters had two bold chalk marks on them:
Reading those tick marks as semaphore flags (as hinted by long-distance, non-electronic communication), they decoded:
which leads them to the Elliott Program Center.
At Elliott, they found two actual semaphore flags and were supposed to notice the confidant across the lake.
When they transmitted the message "WHODUNNIT" in semaphore to the confidant:
he would message back, "MUSTARD":
Teams could then phone in the answer to Game Control
Colonel Mustard, in the Hall, with the Revolver
and finish the game!