Terry Mullins has built his career on detecting liars worldwide. He has administered polygraph tests to Slovakian politicians and Chinese Olympians.

The polygraph, more commonly known as a lie detector, is often viewed as a stunt and pulled out on reality TV shows. However, Mullins is quick to vouch for its effectiveness and routinely uses it to detect theft, fraud, sexual abuse and a multitude of other offences.

To win public support, Mitchell undertook a polygraph test with Mullins in 2013, while being held in Shott’s prison. Controversially, prison officers allowed the test to be filmed on the basis that Mullins signed a non-disclosure form. The form stated that he would not release the video without SPS permission.

Shortly after, the video was approved for release and given to Mitchell’s legal team, who placed it on YouTube. In the almost 17-minute-long video, Mitchell passes the test in which he denies being involved with the murder of Jones.

The former engineer has complete faith in the polygraph test, and it has convinced him that Mitchell is innocent.

He says: “I don't look at the ‘did he do it didn’t he do it’, and I don't want all the arguments going on. What I’m looking for is the evidence. If there is evidence, then they don't need me. If he's clearly done it then he's clearly done it, and he should be punished for it. I've got no time for murderers."

People began to express their support for Mitchell after the polygraph test, which is inadmissible in Scottish courts. However, others were quick to criticise, insisting Mitchell has been able to ‘fool it’. In the video, he answers questions related to the murder of Jodi Jones, with his eyes closed throughout- something which viewers were quick to point out.

“Sky phones me up and says three eminent psychologists claimed he beat the test by closing his eyes and meditating. I asked Luke to close his eyes. The guards were staring in and pulling faces during the test. I didn’t want him to be distracted, I wanted him to ignore them,” he says adding that the three psychologists never identified themselves.

Like many others, I am sceptical of the validity of these instruments. I am told that the test works on the autonomic nervous system which is situated in the medulla at the back of our brains. It works automatically, and affects our blood pressure, respiration, pulse rate, the temperature of our bodies, electro dermal activity and even our urinary tracts. It requires no assistance from ourselves, and it is something which we cannot control.

"There's no secrets or hidden bits. With a polygraph it's all explained. You've already rehearsed these questions and you'll know when they are coming. But if you've got guilt, you can't stop your body. Your body is still going to give you that information, because that's what your body does. Your body doesn't know what fraud, theft, or anything else is. Fight or flight, that's all it comes down to.

“I will say without a doubt that Luke Mitchell did not stab Jodi. End of.”