Maybe this is part of the answer to our question, Where is Mary?

Many people have asked about Chris Pratt, Mary's former boy-friend? Where is he, what is he doing to help the case, why doesn't he participate in helping the family and law enforcement solve the case, and many other questions? One person posted a comment about why Chris would be at a flea market selling Mary's clothing, family pictures, and other intimate items that most people would cherish from a relationship that ended in such tragedy. I can only provide my opinion. Those who know Chris might be able to connect the dots.

A Sociopath
Here is a list of ways to identify a sociopath. This list is from "Profile of a Sociopath". Is is an excellent list of sociopathic indicators.

Glibness/Superficial Charm
Manipulative and Conning
Grandiose Sense of Self
Pathological Lying
Lack of Remorse, Shame or Guilt
Shallow Emotions
Incapacity for Love
Need for Stimulation
Callousness/Lack of Empathy
Poor Behavioral Controls/Impulsive Nature
Early Behavior Problems/Juvenile Delinquency
Irresponsibility/Unreliability
Promiscuous Sexual Behavior/Infidelity
Lack of Realistic Life Plan/Parasitic Lifestyle
Criminal or Entrepreneurial Versatility
Contemptuous of those who seek to understand them
Does not perceive that anything is wrong with them
Authoritarian
Secretive
Paranoid
Only rarely in difficulty with the law, but seeks out situations where their tyrannical behavior will be tolerated, condoned, or admired
Conventional appearance
Goal of enslavement of their victim(s)
Exercises despotic control over every aspect of the victim's life
Has an emotional need to justify their crimes and therefore needs their victim's affirmation (respect, gratitude and love)
Ultimate goal is the creation of a willing victim
Incapable of real human attachment to another
Unable to feel remorse or guilt
Extreme narcissism and grandiose
May state readily that their goal is to rule the world

Here is more input and personal anecdotes from others to help you know if someone is a sociopath:

First, you'll know a sociopath from the description/list posted above here. Also, as another poster wrote, get a book on Sociopaths and it will help you beyond belief. Even a book or article on controlling personalities or borderline personalities will help you. Once you can identify the pattern you will begin to "see the light." Sociopaths are charming at first and may seem charming and normal to everyone around them. But they have an almost scary need for control. They will isolate you from friends and family and you will be tangled in your web before you know it.
The key characteristics of a sociopath include: (1) having no conscience, (2) inability to treat others as human beings, with feelings and rights and (3) inability to learn from experience, from life. One result of this last is gross immaturity, though it may be hidden unless one knows the person well. A sociopath behaves as if he/she were the only person in the whole world and as if everyone else just existed for their benefit and had no existence in their own right. (4) Sociopaths treat other people as toys and hanker after the power to control and hurt their 'nearest and dearest'. (5) Many are monumentally self-important: they may pretend to be millionaires when in reality they are sliding towards financial disaster. (6) Habitual dishonesty.
He will charm his way into your life and heart, then take complete advantage of you - your emotions, your finances, your intellect. He will make you think you are the crazy one. Your friends will see right through him. He will isolate you from your friends and possibly your family. He cannot hold a job and will probably commit crimes - theft, fraud, forgery, and spend time in jail or prison. He will abuse drugs or alcohol. He may abuse you.
My mother is a sociopath, and from all accounts, has been since she was a very young child. She's caused non-stop turmoil in our family, through three generations, and is a charming and frightening menace. I'm the only one to have gotten any counseling on the issue, and the only child so far not to be controlled by mental problems resulting from our upbringing. As such, I'm the 'parent' as far as anybody in our family is concerned, and the dumping ground for complaints about her shocking awful hurtful behavior. I can recognize she never had any kind of 'close' relationship with her father, but it pales in comparison to the way she treated and treats my siblings and myself. Her bad choices in male companionship have contributed to our family grief, but clearly aren't her fault.
The book "The Sociopath Next Door" saved me thousands of dollars in therapy!
It is very difficult to recognize a sociopath but in a nutshell, a sociopath is a parasite. There is no help because a sociopath does not want to be helped. A socipath will attract you with his charm and bring you to his side, then he will toy with you, lie and show no remorse. Sometimes there will be a fake smile in his face while he engages in his malicious ways. When confronted, he will deny any responsibility, then back away from you and blame you for whatever wrong he did. What is worse, everybody will believe him because he is able to gain sympathy in a cunning and calculating way.
My nephew is a sociopath. Growing up he would torture my cat, throwing lighted matches into her bed while she was resting. He would break and hide my mother's belongings and lie about it. One day, she caught him hiding the broken pieces of a porcelain figurine with the other missing objects. He lied to his parents accusing her of hitting him. He came to live with me when he started college. For six months I worked hard trying to make him feel at home. I helped him with his college work, and to get a job. For months I was lied and manipulated. I defended him when his boss accused him of lacking respect and attendance. I believed him when I accused of starting fights, drinking and smoking pot in campus. I even offered to pay for a week's vacation once the semester was over to celebrate his good grades, or at least the good grades he made me believe on. At last I found out he had quit college, had no job and had spent the vacation money. He just turned twenty years old. When I told him that he needed to keep a job and/or study if he wanted to stay with me he moved in with his current girlfriend and told everybody, including my family, that I had thrown him out of my house. Unfortunately they believe him. When I confronted him about his lies he smiled and said nothing.
I'm a little concerned that some people may be labeling everyone who has treated them badly as a 'sociopath'. Here are some examples of sociopathic behavior: 1. A member of the family develops a nose bleed. The sociopath's first reaction: 'How dare you bleed on my carpet?' 2. Husband faints in wife's presence. Her sociopathic reaction as she steps over his body: 'Hell! That means I'll have to collect the kids from school today'. 3. Mother makes singularly vile false allegations, such as rape, against her own son and calls the police. When the police point out there's no evidence to support her accusation, she says, 'But I feel just oh-so-violated', as if that constituted evidence. 4. Teenage daughter is diagnosed as suffering from schizophrenia. When the psychiatrist orders inpatient treatment at a mental hospital with a special unit for teenagers, the sociopathic mother tries to prevent her going to hospital. When the father takes their daughter to the mental hospital, the mother threatens to abduct her! She tries to phone her daughter in hospital daily and subjects her to emotional blackmail.
A number of mind-controlling cult leaders may exhibit many of the behavioral characteristics of a sociopath -- an outstanding ability to charm and seduce followers. Since they appear apparently normal, they are not easily recognizable as deviant or disturbed. Although only a trained professional can make a diagnosis of whether or not someone is a sociopath, it is important to be able to recognize the personality type in order to avoid further abuse. These traits also apply to a one-on-one cults relationship. ... Glibness/Superficial Charm ... Manipulative and Conning ... Grandiose Sense of Self ... Pathological Lying ... Lack of Remorse, Shame or Guilt ... Shallow Emotions ... Incapacity for Love ... Need for Stimulation ... Callousness/Lack of Empathy ... Poor Behavioral Controls/Impulsive Nature ... Early Behavior Problems/Juvenile Delinquency ... Irresponsibility/Unreliability ... Promiscuous Sexual Behavior/Infidelity ... Lack of Realistic Life Plan/Parasitic Lifestyle ... Criminal or Entrepreneurial Versatility

A sociopath does not have to be a person that is constantly in and out of jail, failing in being able to keep a job, nor constantly being broke. Sociopath's can be wealthy, have a great history in the work place and have never had any run in with the police. What they do have is the ability to manipulate each situation to where nothing is their fault. They are quick to give praise to someone, but use that as another way to draw them further under their control. They truly have no capacity to believe that anything they have ever done is wrong - even when caught in a bold faced lie.
They don't preplan their "sociopathness" and how it will effect what they want - sociopath's are naturally that way. They are the way they are - to everyone in their lives - from when they were a child, throughout their entire lives. They do not have the ability to change the way they are. They may "mellow" as they age, but their need to have control over others, the need to be impulsive, their feelings that, even in lying, they never do anything wrong, and their ability to charm everyone they think they need to charm, does not leave them as they age.
It's also very hard for someone involved with a sociopath to be able to see what they know is happening, even after catching the sociopath in the lies and manipulation. It's incredibly hard to decide to leave a sociopath, as well as stay away from that sociopath.

This article was from Profile of a Sociopath