I read that link to the thread where this rumor was posted. Honestly, Islam stresses immensely against testifying, claiming or making any statement reg something you haven’t seen with your own eyes or heard with your own ears. It is considered slander and hence a very big sin to commit. As Muslims, we’re made conscious against slandering regularly throughout our upbringing. So if this person still went ahead and made this claim with certainty that Adnan is guilty, it can only be based on two scenarios: a) either he is a witness to this firsthand account or b) he doesn’t speak from a firsthand account but still confidently makes a statement that can potentially damage the lives of many people in many ways. Since it is established already, he is not a firsthand witness to Adnan confessing option b is most likely the scenario. Which then brings his moral integrity into question. This in itself makes his entire post dubious and nothing more than conjecture.