Your job is not to make a hiring decision—it’s to contribute to the pool of knowledge to paint a picture of the candidate and make sure the group has the right signal to make a decision.
Understanding the "why" behind the facts will help you create a picture. When interviewing, constantly ask yourself “why”. Stop digging only when there is no more “why” to ask.
Low-confidence interviewers are often tempted to ask questions that attempt to make them look smart. The reality is that, for a deep-dive interview, the key is not to ask esoteric questions. The key is to get the candidate talking about a project, experience or achievement that is fresh in the memory and relevant, and then to actively and critically listen to ask the right follow-up questions that help you meet the objective of discovering. The questions themselves should almost always be simple.