Criminal Intent
Since I haven't owned a TV in a decade I get my TV series in heavy doses on DVD. I've been pretty hooked to Law and Order:CI and before I was past the first season I started to see broad patterns on how to convert a hunch into incriminating evidence.
You have to be as cool as detective Goren to get that hunch but that really is only half the battle. The other half is incrimination.
Here is "How to Incriminate your Suspect for Dummies". And trust me I've given it very little thought but at the end I suggest a perfect crime nonetheless.
The React Trap:
Detectives casually mentions to defendant something only he cares about as the one who executed the crime (like a piece of critical evidence they need) and if he gives a reaction under surveillance(a covert phone call, a digging session in the backyard) he incriminates himself.
A slight variation is that detectives falsely accuse somebody else thats the real criminal has a motive to protect which provides the stimulus for the reaction (the reaction ihere s usually an anonymous claim to the police with hard evidence of having committed the crime, to let the accused off the hook)
The details here can be absolutely intriguing.
The Verbal Slip
The detective earnestly engages the criminal in a discussion about the circumstances of the crime without giving any hints that he is under suspicion.
The criminal drops his guard and forgets the difference between what he should pretend to know as a casual 3rd party and as somebody who actually knows a great detail about the circumstances of the crime (timelines, place, motives etc)
The first time this happens it seems like a really cool device but heck that's at the heart of what makes lying a hard thing to do! Think twice about everything.
The Prisoner's dilemma:
You pbbly know what this is all about. Detectives play conspirators off against each other. Look up the game theory on this if you havent.
Pushing buttons:
My least favorite technique for its crudeness. Get a confession by confronting the suspect with psychological truths about him that he is very insecure about and thinks are carefully hidden or by placing dramatic artifacts from the crime or past crimes when they are least expected
Predictive surveillance:
Establish a pattern to the crime that lets you predict the next victim or scene of crime and catch him in the act
The Secret Motive:
This is rare but wows me because you leverage out a confession that you know is not truthful yet with the same result.
This involves uncovering that the motive for crime is to keep an important secret (like something very detrimental to a loved one or the criminal himself) and even if it cannot be proven in court by simply making it public on a trail the criminal's original intent is overriden.
He is asked to confesses to the crime on some other fake grounds since the detective's dont really care, the punishment is likely similar.
That got me thinking about the perfect crime and it almost happens in the "Enemy Within".
The idea is to commit the crime without doing anything criminal. In other words, to borrow a cyber security term, socially engineer the crime by creating a situation where you give another person or persons a different motive to commit the same crime. To do so you may have to commit a much smaller crime (to seed mistrust, fear whatever) or just be a manipulative yet non-violent sociopath.
Peace :)