This is a very hard question actually. Interviews are pretty subjective process. It will be very hard to summarize what are the possible reasons to hire/reject candidates.

Aside from answering the author's question, I would propose the onsite in-person interview should be video recorded, conducted by one interviewer. Then later replaying in the hiring committee or what so ever, and vote for hire/no hire. That could eliminate any discrimination/bias/subjective/personal feedback from interviewer and stop interviewee from being accusing any accidents during the process.