Murder is an unthinkable act for most, but the motive behind committing murder generally starts from an emotion. However, when we talk about the motives of serial killers, it's a whole different story.

Understanding the motivation behind a brutal murder is crucial not only for detectives seeking the perpetrator but also for the families of the victims and even for the public. In the aftermath of what seems like a senseless murder or a series of murders, people often are left with one question: why?

While the motives behind most crimes might initially be hard to decipher, detectives and psychologists generally agree that the 'why' can usually be narrowed down to three or four possible motives. They range from jealousy to greed.

Though the most basic, immediate 'why' of a murder can often be quickly determined, the deeper motivations—what actually pushed the person over the edge to violence—are not so easy to uncover.

The 'whys' that are hard to answer are the less obvious ones and those that are hardest for us to understand. Motive is the reason, the why, sometimes the darkest chapter in the darkest book in the vast library we call the human mind."

Several detectives claim that all murders stem from financial greed, lust, or the pursuit of power. To those who pose the question of whether there isn't a fourth category, what about jealousy? What about anger? They answer: You're asking the wrong question. You should actually ask: What causes the jealousy or anger? There are only three possible answers to this question: financial greed, lust, or the pursuit of power. And so, we come back to just three motives for committing murder.

Meanwhile, others argue that there are indeed four possible motives for murder: lust, love, hate, or money.

The motive of lust lies behind someone murdering a romantic rival, as well as 'thrill killers' who murder for an erotic charge or sexual reward. A murder motivated by love, for example, could be mercy killing a partner with a terminal illness. Hate can be directed at an individual, a group, or a culture. While murdering for money may involve pursuing an inheritance or insurance payout.

But finding a motive for murder doesn't go far enough to explain the murder. Most people experience lust, love, or hate at some point, and most people seek money in terms of wanting financial freedom. However, the vast majority of people do not commit murder.

In a published report, the FBI notes that when it comes to serial killers, determining the motive can be much more difficult—and perhaps not as crucial to the investigation as one might think.

According to the FBI report, a serial killer's crime scene can have bizarre characteristics that can obscure the identification of a motive. The behavior of a serial killer at a crime scene can evolve during the series of crimes and show different interactions between an offender and a victim. It's also extremely difficult to identify a single motive when more than one perpetrator is involved in the murders.

The FBI further noted that even if a motive can be identified, it may not necessarily help in identifying the actual killer. Researchers also caution that investing too many resources in determining a serial killer's motive might derail the investigation.

The FBI compiled the following list of possible motives for serial killers:

• Anger, directed towards a specific subgroup of people or society as a whole.
• Criminal enterprise, where the killer financially or in status benefits from murder within organized crime or drug trafficking.
• Financial gain, including murders during robberies, insurance fraud, or welfare.
• Ideology, to further the goals of a specific individual or group; terrorist attacks and some hate crimes might fit here.
• Power/sensation, where the killer becomes more powerful or excited when they commit murder.
• Psychosis may encompass severe mental disorders as well as auditory or visual hallucinations and paranoid or grandiose delusions.
• Sexual desires can also be a motivator, and the FBI noted that there doesn't necessarily need to be overt sexual contact at the crime scene for this to be a motive.