Psychologists, researchers, and experts in the field of investigation agree that a vast majority of the time people feel discomfort when telling a lie about a significant subject. The easiest approach to not telling an outright lie is to leave out a detail or specific action connected with the truth.
Often when you question someone to understand what happened, you will hear, "and that's about all." This phrase is a clear indicator that more happened that the person, for whatever reason, does not want to share with you. Focus your questions around what preceded that phrase, and you are likely to uncover more important parts of the story.
If you have specific questions about detecting deception and finding the truth, please post them here. Or, for a confidential assessment, contact Julia Bate at firstname.lastname@example.org.