When people try to conceal information they 'drop breadcrumbs'. (Hansel and Gretel did it in the hope of finding their way home.)
Here's how to spot a trail of crumbs. Imagine you want to know if your children have concocted a story together, or if your staff are telling the truth about an event. Listen out for identical phrases of five or more words. If you find these identical sentences in several peoples' versions of events you probably have some element of collusion.
Logically we think that if we all witnessed the same thing we would all give exactly the same account, but it's not true. The chances that we will replicate a complete sentence or phrase are actually incredibly low.
Follow the breadcrumbs to get to the truth.