It is thought that 1 per cent of adults are psychopaths.
The number might seem small at first (look on the bright side: 99 per cent of us are not), but it still translates into about 75 million people.
Psychopathy, a term often used interchangeably with sociopathy, reflects in a disregard for laws, social conduct and the rights of others. In more extreme cases, it also comes with a failure to feel remorse or guilt and a tendency towards violent behaviour.
People under 18 cannot be labelled psychopaths by professionals. However, in 2013, the American Psychiatric Association added a new condition called "conduct disorder with callous and unemotional traits", for children aged 12 and over, which can be seen as a precursor to psychopathy.
A report from 2001 in the journal American Family Physician stated that approximately 6 to 16 per cent of boys and 2 to 9 per cent of girls meet the criteria for a diagnosis of "conduct disorder", which can lead to psychopathy.
Several reports on the Florida shooter, 19-year-old Nikolas Cruz, mention potential early traits of psychopathy, including reports of him abusing animals as a child.
"Psychopaths don't just appear when they are 20. They are always different from an early age," Kent Kiehl, a psychology professor at the University of New Mexico and the author of The Psychopath Whisperer, told the NY Post.
So how do you know?
According to the Hare Psychopathy Checklist Youth Version, considered the "gold standard" in assessing psychopathy, there are some obvious signs that can potentially mean your child is growing up to be a psychopath.
These signs include lack of empathy, lack of guilt or regret, pathological lying, grandiose sense of self-worth and a failure to take responsibilities for their actions, especially when it comes to fighting and bullying.
"Individuals who score high on those traits are more likely to produce further violence," Kiehl told the Post. "If they are sanctioned but continue on the same path, it's not a perfect indicator, but it's enough to cause concern."
Another aspect to highlight is the extremely high chance of a psychopath giving birth to another psychopath, as psychopathy is hereditary approximately half the time.
Whether or not someone is a psychopath is not just a matter of opinion. Psychopaths have been found to have differently structured brains to other people.
A 2014 study found a lack of gray matter in the brain of psychopaths, near the region responsible for processing emotions. They also found that the area of the brain responsible for reacting to excitement and thrills was overactive.
There is no known cure for psychopathy or conduct disorder.
However, experts believe early intervention can reduce harm - and this can start as early as 2 or 3 years old.
Intervention is in the form of therapy, which experts defend should involve rewards for good behaviour rather than punishment for bad actions.
Paul Frick, a psychology professor at Louisiana State University and the author of Conduct Disorder and Severe Antisocial Behaviour, told the Post that "emotion coaching" can help parents and therapists show children how to pay attention to the feelings of others.
"By saying: 'Can you see how Johnny is feeling?' [when a toy is snatched from him] and getting them to respond correctly, you can motivate them. You give them a star or a sticker as an incentive.
"Even though it doesn't come naturally to them, they can learn others' perspectives."
Children as young as 3 can show signs of being callous and having conduct disorder. If faced with a crying peer, typical children will either try to comfort them or take flight. Children with conduct disorder will show no emotion towards the crying child.
The behaviour can manifest itself even earlier. Researchers at King's College London tested 200 babies aged 5 months to track whether they preferred looking at a person's face or at a red ball. Those who favoured the ball displayed more callous traits two and a half years later.