Famous Crimes Where Polygraph Tests Were Administered

Polygraph examinations in Knoxville can be used for a variety of different purposes, from resolving issues in personal relationships to uncovering corporate espionage and everything in between. However, most people associate polygraph examinations in Knoxville with criminal investigations! Over the years, polygraph has played a crucial role in many well-known cases. Let's look at some instances where polygraph exams played a part in criminal cases.

What is a Polygraph Exam?

A polygraph exam, commonly known as a lie detector test, is a procedure used to measure physiological responses that are believed to be associated with truthfulness or deception. The polygraph instrument records several physiological indicators while a person is asked a series of questions. The most common physiological parameters measured during polygraph examinations in Knoxville include:

  • Heart Rate: The number of times the heart beats every minute.
  • Blood Pressure: The force that blood exerts on the artery walls.
  • Respiration Rate: The rate at which a person breathes.
  • Galvanic Skin Response (GSR): Changes in the skin's electrical conductivity can be influenced by sweating.

Famous Polygraph Exams

There have been many high-profile cases where polygraph examinations were utilized to verify information or otherwise aid the investigation. In most states, polygraph is not admissable in court, but as demonstrated by some of the cases we will be discussing, they can be useful in eliminating suspects allowing the investigation to take a different path. Let's take a look at a few of the famous cases that feature at least one polygraph exam.

Elizabeth Smart Kidnapping (2002)

Elizabeth Smart, a teenage girl from Utah, was kidnapped from her home in 2002. During the investigation, the police administered polygraph tests to various individuals, including Richard Ricci, a handyman who had worked for the Smart family. Although Ricci initially passed the polygraph, he remained a suspect. Ultimately, he was not connected to the kidnapping, and the perpetrator turned out to be Brian David Mitchell.

Natalee Holloway Disappearance (2005)

Natalee Holloway, an American teenager, disappeared from Aruba during a high school graduation trip. The investigation involved polygraph tests for several individuals, including suspects Joran van der Sloot and brothers Deepak and Satish Kalpoe. The results were inconclusive, and the case remains unsolved.

The Weleetka Murders (2008)

The Weleetka Murders were one of the most notorious cases in 2008, and it was solved thanks to the use of polygraph! During the investigation into the murder of his fiancee Ashley Taylor, Oklahoma police polygraphed Kevin Sweat. As a result of the exam, police searched some land owned by Sweat’s father. Not only did they discover Ashley’s remains, they also found .40 caliber casings that matched the gun used in the unsolved murder of Taylor Paschal-Placker. Sweat was not even a suspect until taking that polygraph and was ultimately charge with both murders.

Zodiac Killer (Late 1960s to 1970s)

The Zodiac Killer, a serial killer who operated in Northern California during the late 1960s and 1970s, taunted law enforcement with cryptic letters and ciphers. While the police conducted investigations and interviews, including polygraph tests to eliminate potential suspects, the Zodiac Killer was never caught, and his identity remains unknown.

Joseph Cambron (2014)

In September of 2014, detectives in Louisville conducted a polygraph exam on 21 year old Joesph Cambron in connection with the murder of 12-year-old Ray Allen Etheridge. The polygraph showed that he was involved in the stabbing and although not admissible in court, when faced with the polygraph results Cambron confessed. Coupled with evidence from witnesses this led to his arrest.

Murder of Jodi Jones (2003)

This next case is a little different in that a polygraph examination may actually have proven a young man's innocence. In 2003, 14-year-old Luke Mitchell was arrested for the brutal murder of his girlfriend, Jodi Jones. From the very beginning, Mitchell pleaded not guilty, submitting a special defense of alibi, stating that he was at home at the time of Jodi's death. While no genetic material that their existing relationship could not explain was found, and the murder weapon was never recovered, he was found guilty primarily based on his being the one to discover Jodi's body. Mitchell was sentenced to life imprisonment with a minimum 20-year sentence. Multiple appeals have been launched on his behalf, and he continues to protest his innocence; it was even ruled that the police had breached his human rights during the investigation. In 2013, Mitchell passed a polygraph during which he denied being involved in the murder. However, as polygraph examinations are not admissible in court in Scotland, it only served to gain public support, and at this time, he remains incarcerated, although he may be granted parole in 2025.

Jeffrey MacDonald Case (1970)

Jeffrey MacDonald, a former Green Beret doctor, was accused of murdering his pregnant wife and two young daughters in their home at Fort Bragg, North Carolina. MacDonald underwent a polygraph test, and the examiner concluded that he was being deceptive. However, the polygraph results were not conclusive, and MacDonald's case has been highly controversial, with ongoing debates about his guilt or innocence.

Gary Ridgway, the Green River Killer (1984)

Gary Ridgway, one of the most notorious serial killers in U.S. history, underwent a polygraph test early in the investigation. Ridgway initially passed the polygraph, but he later confessed to the murders of numerous women, leading to his conviction. It's important to note that the polygraph results did not prevent further investigation and the eventual confession.

Adrian Prout (2007)

Millionaire Adrian Prout actually took a polygraph in 2012 when his fiancee arranged it in an attempt to prove his innocence in the murder of his wife Kate Prout in 2007. However, this would ultimately backfire as he failed the polygraph and on hearing the result Prout is said to have stood up and with no emotion or remorse told the detectives that the test was correct. Prout was sentenced to a minimum of 18 years.

Chris Watts (2018)

In 2018, Chris Watts murdered his pregnant wife Shanann and their daughters Bella and Celeste. Watts maintained that he had no idea what happened and that he believed his wife had left him, taking the children. However, when a polygraph was used to question him about his role in her disappearance and if he had physically harmed his wife and children, he failed with an unusually low score. After failing the polygraph exam, he requested to talk with his father to whom he confessed to killing his wife, although he initially claimed that it was Shanann who hurt the children. He later led police to the bodies and was convicted of all three murders.

When you find yourself considering polygraph examinations in Knoxville, it is unlikely to be because you are involved in a high-profile criminal investigation - although we can help if you are! At Kendall Investigations, we can assist with polygraph examinations in Knoxville for a variety of situations, including infidelity, child custody or divorce hearings, corporate espionage and fraud, and even pre-employment screening. No matter how big or small the case, every client who visits us for polygraph examinations in Knoxville is treated with the same level of compassion and integrity.

Uncover the truth!


Ken Shull served as a Special Agent with the FBI for almost 25 years and was head of the FBI Polygraph program until his retirement in 2001. At that time he set up the Kendall Investigations practice as a private investigator in Knoxville, TN offering Polygraph services, private investigations, and security guards. Ken is a member of the American Polygraph Association and The American Association of Police Polygraphists.

The Truth is Still the Truth Even if No One Believes it, A Lie is Still a Lie Even if Everyone Believes it.