Tuesday, April 24, 2012

Arches & Loops & Whorls--Oh My!

What the Dewey Decimal System does for books, the Henry System does for fingerprint identification.

But what, exactly, is a fingerprint?

The pads of a person's fingers display grooves and friction ridges which provide traction, allowing a person to pick things up without having everything literally slip through his or her fingers.  This is good. Forensically speaking, what's even better, is that these markings are distinct and identifiable.

As early as 1685, a Bolognese anatomy professor identified loops and whorls on a person's finger pads.  That was expanded upon by the work of Sir Edward Henry who divided fingerprints into five types as early as 1899 and whose efforts became the basis for modern classification.

No two people (yes, including otherwise identical twins) have exactly the same fingerprints.  Fingerprints are divided into three basic categories: arches, loops and whorls.  The basic categories are then further subdivided based on characteristics of the markings.  For example, only 5% of the population display arches and an arch can be either plain or tented.  Loops are encountered in 60% of the population and can be single or double. Depending on the direction the loop leans, they are described as either radial or ulnar.  The remaining population has target or spiral whorls that have four subgroups: plain, central, double or accidental.

It used to be that to compare prints one had to have a good magnifying glass and a lot of patience.  Now the Automated Fingerprint Identification System (AFIS) can search over 500,000 prints in less than a second.  AFIS will provide requesting law enforcement agencies with possible results that must then be hand verified to ensure accuracy.  Returns from AFIS usually occur within an hour, making this one of the few clues that an investigator can follow up on and have almost instantaneous results.

An investigator looks for three types of prints at a crime scene: patent, plastic or latent.  A patent print is visible to the naked eye and occurs when a substance on the finger is transferred to another surface.  The most obvious example is when a person has their fingerprints rolled across an inked pad and then across a piece of paper.  It is the ink that leaves a patent print behind.

The second type of print is plastic.  This is when the finger comes in contact with a soft malleable substance. Think wax, soap or even a thick layer of dust.

The final type is latent.  This print is invisible without specialized equipment such as a laser, ultraviolet light or special processing.

Rarely can a person rid themselves of their fingerprints as the body rejuvenates itself and keeps the same pattern.  Deep gashes or other scars may obliterate a pattern, however, the damage leaves its own distinctive marks.  For story purposes, it's also handy to note that after wearing latex gloves for awhile, a person may leave prints through the material.  Leather glove also leaves impressions distinctive to the glove.

Prints can place a person at a crime scene, or in possession of a weapon.  It's pretty nifty that they can be used to positively identify a specific individual.

Monday, April 16, 2012

I'm From The Government, And I'm Here To Help...

What's wrong with this scene?


The man rapped his knuckles against the oak door and waited. A wizened woman answered the door wearing a muumuu and a confused look on her face.  
"Good afternoon, Ma'am," he said. I'm Lieutenant Mitchell with the FBI. Do you mind if we talk?"


If you keyed on the muumuu as an outdated fashion choice, please stop reading. This post will not help you. If, however, you continued writing this scene in your mind and you have the woman slam the door in the face of the impostor, congratulations, you may stop reading. You don't need this post. Lastly, if you are scratching your head, unable to answer the question, please, please, please continue reading.


The answer? The Federal Bureau of Investigations doesn't have the rank of lieutenant in its hierarchy.  


Recently, I've read several books where the hero of the tale is an FBI lieutenant. The moment I encountered the gaffe, I lost all confidence in the author. To me, this is analogous to becoming a veterinarian because you love children. 


The problem is the authors didn't know their character's background. It's not enough for characters to be a cop. What kind are they? What is their jurisdiction?  What do they do? Even within agencies, job duties can be vastly different. 


Exhibit A.


This link is a mere click away at Wikipedia. Imagine what a person can learn by going to the actual source....

Officers of the FBI are not officers, they are agents. At the beginning of their careers, they start as a Probationary Agent. From there, they can ascend as follows:

  • Special Agent
  • Senior Special Agent
  • Supervisory Special Agent
  • Assistant Special Agent-in-Charge (ASAC)
  • Special Agent-in-Charge (SAC)
  • Assistant Director
  • Associate Executive Assistant Director
  • Executive Assistant Director
  • Deputy Chief of Staff
  • Chief of Staff & Senior Counsel to the Director
  • Associate Deputy Director
  • Deputy Director
  • Director

The authority and focus of the FBI is vast. This appeals to writers who want their characters to be able to investigate a broad selection of crimes-- both against the nation and in the FBI's mission to support the efforts of state and local jurisdictions.

There is a tremendous amount of information available regarding the FBI -- more than an author will ever work into his story.  But get the basics wrong and every other detail in the novel becomes suspect.


Monday, April 9, 2012

I Hear You Knocking, But You Can't Come In....

Law enforcement is a bit of a dichotomy: Police officers operate with great latitude within strict parameters. In other words, how officers performs their job can be quite diverse as long as they stay within certain legal constraints. Cases can be won or lost because of warrants. Despite all the impromptu door busting that occurs on television, there are few situations where officers can legally force entry without a warrant.

The 4th Amendment to the US Constitution protects against unreasonable search and seizure and requires police officers to obtain a judicially reviewed and sanctioned warrant based on probable cause before they have the authority to search a place or person or seize either.

So how can so many TV shows be wrong? Well, sometimes, they're not.

Interpreting the Constitution keeps a whole slew of people employed and case law is a moving target, but there are certain exceptions to the warrant requirement that police officers routinely use.  If the person gives consent to search, the officer may. Motor vehicles have a diminished expectation of privacy. If contraband is in plain view, an officer can seize it.  Likewise, if an officer is in an area usually afforded protection (i.e. a person's house) and he sees contraband, he can seize it, and by extension, make the appropriate arrests provided the officer had a legitimate right to be there in the first place.

Starting to get a little confusing, no?

An officer can cite exigent circumstances to support a warrantless entry and search.  This involves imminent danger where the officer feels intervention is required to save life or property.  For example, officers respond to a domestic violence call.  As they near the door, they hear a scream from within the house. The door is locked, no one answers when they pound on it, and in the officers' minds, if they don't take immediate action, someone's life is in peril.  Officers kick the door, break a window, or whatever they need to do to get in. The circumstances they encounter inside, will determine how they proceed.  If they encounter a woman holding a smoking gun over her just-killed husband, they will take her into custody, but then obtain a search warrant to process the whole crime scene. Why? Because defense attorneys will argue that any evidence obtained without a warrant should be suppressed.  In this scenario, the defense would argue that since the exigency (saving a life)  no longer exists (since sadly, hubby is deceased),  it can no longer be claimed.  It becomes the State's responsibility to justify the officers' deviation from the warrant requirement, so to be safe, prudent officers err on the side of getting a warrant even if a legal loophole nullifies the need.

Easy, right?  Yeah, try waking a judge at three in the morning.

The most common result of an illegal search or seizure results in suppressed evidence. Obviously, this can be catastrophic to the prosecution.  A good defense attorney will always attack the legality of a search.

Officers must have a working knowledge of how to conduct themselves to operate within the law they have sworn to uphold.  Writers must also possess a broad understanding of the law so they can create believable scenarios and control when and if their characters step over the line.