User blog comment:AltertheSilverBird/Total Drama: Danganronpa Chapter 8: Class Trial/@comment-27060311-20161002211959/@comment-27060311-20161002212328

And now let me explain what happened:

Both Goeff and Bridgette entered the tower and probably Topher there, I think by accident Bridgette hit Topher with the surfboard and knocked out Topher, Geoff then probably to defend his girlfriend of being executed used the medicine on Bridgette and knocked her out as well after they watch the consquences with Tyler's event.

Geoff then returned to the crime scene and finished the service by disposing of the body, however he didn't knew that Topher still alive and this resulted in Geoff killing Topher in the process, at least what I think what happened.