Many of them show signs of antisocial behavior from an early age. They might not be able to form normal relationships and lack empathy. Like the serial killers who can kill without any remorse or consideration for their victims' feelings. They may also be loners who isolate themselves from society.
Often, they have a history of abuse, either physical or psychological. For example, some killers were abused as children, which can lead to deep - seated anger and a distorted view of the world. They may also have problems with impulse control.
Substance abuse can also be a factor. Some people who are addicted to drugs or alcohol are more likely to be involved in violent situations that can lead to murder. Their judgment is clouded, and they may act on sudden urges without thinking about the consequences.