Unfortunately, lie detection isn't always as easy as it is made out to be on TV and in the movies. A lot of lie-detection methods aren't overly reliable, and as such many aren't admissible in court proceedings. However, at the conference I recently went to in New York (details here) I got to hear about some exciting lie-detection research that is very promising.
Lying to someone actually involves a lot of cognitive processes, all operating at once. This is because not only do you need to keep your 'story' in working memory to make sure it stays consistent, you have to monitor your body language and voice pitch to make sure you're not giving off signs that you're lying (e.g. What's the appropriate level of eye contact? Is my voice shaky and all over the place? I should try not to look nervous... etc.). Additionally, you need to constantly monitor the person you're lying to, to make sure they believe you. So Prof. Aldert Vrij and others have been working on making police interviews more cognitively demanding, so that verbal and non-verbal cues of deception are more likely to leak out, due to the liars having fewer resources to cope with the demanding nature of the interview.
A few lie detection 'tips':
A lot of people 'know' that liars avoid eye contact. However this may not be true; since this is so commonly known, liars may try to keep eye contact to make sure it doesn't look like they're lying (and so they can check you're believing them).
Another thing people 'know': liars fidget. Again because people are aware of this, sometimes liars may instead be trying very hard to control all their body movements and appear very rigid. Additionally, fidgeting usually indicates nervousness. What if the liar just isn't nervous?
Some people think liars will have more speech errors: "umm, ahh" etc. However in some cases, rehearsed stories may come out smoother, without these errors.
As you can see, these tips aren't overly helpful, because people react in different ways. All I've really demonstrated is that looking for common signs of lying are probably somewhat pointless, if the liars know those signs too. So they may look at you, or look away. They may fidget, or be perfectly still. In a lot of cases, if you're in a situation where you're accusing someone of lying, a truth teller is still probably going to be nervous, and just as interested in making sure you think they're telling the truth. So this means they could act in very similar ways to a liar!
There are actually much more helpful indicators of lying out there, but I'm not going to tell you them, sorry! Although I trust all my readers are truthful beings (...right?) I don't want to teach people to be better liars. So I've only talked about information that is readily available on the internet anyway. It's important that police are still able to have the upper hand in interviews so that they can catch criminals!
P.S. I'm not saying the show Lie to Me was that inaccurate. Research suggests a very small proportion of people may in fact be 'Truth Wizards' that are able to detect subtle microexpressions and pick out liars. How cool it that!?
P.P.S. This blog: Eyes for Lies, apparently belongs to one of the people who has been identified as a truth wizard, and claims to have a 96.9% accuracy rate in lie and truth detection. She gives her take on some high profile cases. Very interesting.