When you are questioning someone about their activity or an incident they were involved in or witnessed and they don't want to be completely truthful, what they choose to hide or withhold from you will influence what they actually tell you. This will be evident within their word choices, what they say and how they say it. It is human nature. You just have to train yourself as to what to look for and how to question further. Here is an article that goes a little deeper into Missing Information Within Written Statements.
What people don't want to tell you will influence what they actually tell you. Learn to see what people are withholding from you.— Wesley Clark (@WesClark) June 14, 2013