Tell-tale signs that can give away a killer including 'how often they blink'

Creepy tell-tale signs and traits which expose hardened murderers include how often they blink and their body language, a behavioural scientist said.

Cliff Lansley, an experienced scientific advisor, explained the tricks experts use to spot whether a killer is lying.

Mr Lansey said even the "most confident, hardened killers" can slip up, particularly during police interviews when their behaviour typically changes.

At the beginning of an interrogation, a interviewer may hold a conversation with a suspect which makes them feel comfortable, Mr Lansey said, like family, skills, education and their dreams.

During this conversation, the interviewer notes "how often they blink, the normal colour of their skin, their speech rate and how they maintain eye contact."

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Mr Lansey added: "Later on, when the real questioning begins, we can assess changes to these normal baseline patterns to assess discomfort, stress and lying."

But some criminals might use eye contact to gauge whether the interrogator is buying their story, while others may try and avoid it altogether.

So, Mr Lansey said when police interview potential suspects, they are trained to question them in such a way as to reveal their innermost feelings and thoughts.

And while we may be accustomed to believe that someone looking away from you means that their lying, this is actually not true, the expert continued.

"Studies show that maintaining eye contact while telling an account is actually a stronger indicator of deception than looking away, since this suggests someone is checking to see if they are being believed," Mr Lansey explained.

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He spoke to Hippocratic Post, which also alluded to a study conducted in 1971 by social psychologist Professor Albert Mehrabian at the University of Los Angeles. It showed then that body language makes up for 55 per cent of the meaning in how someone communicated their feelings.

And around 38 per cent came from the tone, pitch and pace they used, while just seven per cent came from the actual words.

Mr Lansey explained how the behavioural science has changed somewhat since Prof Mehrabian's work, but core beliefs around body language remain similiar.