Forensic document analysis:
Written communications (i.e. ransom notes, threats, letters, emails, suicide notes, a profile of a serial killer communiques, etc.) can be examined for unconscious communication.
Ransom note left at crime scene reveals another story (see JonBenet case)
Suicide note reveals a homicide (see O.J. Simpson case)
Letters received from a “helpful” person in an unsolved murder reveals perpetrator
Communication from a profile of a serial killer reveals (between the lines) he’s on verge of killing.
Letter from convicted felon uncounsciously reveals mitigating circumstances
Interrogations and other verbal communications with a suspect
Interrogators can listen for unconscious confessions and clues. They can ask questions that keep the suspect on the same train on unconscious thought.
In O.J. Simpsons recorded interrogation by the LAPD 13 hours after his ex-wife’s murder his thoughtprints strongly suggested that he was a high risk to run in an effort to escape prosecution. He ran four days later.
Interrogators trained to understand unconscious communication could have noticed the warning and arrested him quietly without incident and prevented chase.
Learn more about thoughprint profiling in the O.J. Simpson trial.
Analysis of a suspects communications can be used to demonstrate innocence or guilt. Just as someone can unconsciously confess, they can unconsciously explain their innocence or significant mitigating circumstances.
A first-time offender found guilty and given an excessive sentence can unconsciously communicate information revealing special circumstances that affected their judgment. This type of information can be useful in appealing the sentence and establishing that they are not a danger to society.
Someone charged with murder triggered by the aggression of the victim may have overreacted in self-defense in light of a severe previous assault.