Really bad Vocational Guidance Counselors.

Found this on wikipedia thought in was interesting

The motives of serial killers are generally placed into four categories: "visionary", "mission-oriented", "hedonistic" and "power/control"; however, there is often considerable overlap among these categories.[

Visionary

Visionary serial killers suffer from psychotic breaks with reality, sometimes believing they are another person or are compelled to murder by entities such as the devil or God.] The two most common subgroups are "demon mandated" and "God mandated".

Herbert Mullin believed the American casualties in the Vietnam War were preventing California from experiencing an earthquake. As the war wound down, Mullin claimed his father instructed him via telepathy to raise the amount of "human sacrifices to nature" in order to delay a catastrophic earthquake that would plunge California into the ocean.

David Berkowitz is an example of a demon-mandated visionary killer. He claimed a demon transmitted orders through his neighbor's dog instructing him to murder.

Mission-oriented

Mission-oriented killers justify their acts on the basis that they are getting rid of a certain type of person, such as homosexuals, prostitutes, blacks or Catholics, whom they find undesirable; however, they are not psychotic.

Ted Kaczynski, the "Unabomber", targeted universities and the airline industry.[26] He wrote a manifesto that he distributed to the media, in which he claimed he wanted society to return to a time when technology was not a threat to its future, asserting that "the Industrial Revolution and its consequences have been a disaster for the human race."

Hedonistic

This type of serial killer seeks thrills and derives pleasure from killing, seeing people as objects for their enjoyment. Forensic psychologists have identified three subtypes of the hedonistic killer: "lust", "thrill" and "comfort".

Lust

Sex is the primary motive of lust killers, whether or not the victims are dead, and fantasy plays a large role in their killings. Their sexual gratification depends on the amount of torture and mutilation they perform on their victims. They usually use weapons that require close contact with the victims, such as knives or hands. As lust killers continue with their murders, the time between killings decreases or the required level of stimulation increases, sometimes both.

Kenneth Bianchi, one of the "Hillside Stranglers", murdered women and girls of different ages, races and appearance because his sexual urges required different types of stimulation and increasing intensity.

Jeffrey Dahmer searched for his perfect fantasy lover—beautiful and eternal. As his desire to find the perfect lover increased, he experimented with drugs, alcohol and exotic sex. His increasing need for stimulation was demonstrated by the dismemberment of victims, whose heads and genitals he preserved. He experimented with cannibalism to ensure his victims would always be a part of him.

Thrill

The primary motive of a thrill killer is to induce pain or create terror in their victims, which provides stimulation and excitement for the killer. They seek the adrenalin rush provided by hunting and killing victims. Thrill killers murder only for the kill; usually the attack is not prolonged, and there is no sexual aspect. Usually the victims are strangers, although the killer may have followed them for a period of time. Thrill killers can abstain from killing for long periods of time and become more successful at killing as they refine their murder methods. Many attempt to commit the perfect crime and believe they will not be caught.

Robert Hansen took his victims to a secluded area, where he would let them loose then hunt and kill them.[32] Lee Boyd Malvo and John Allen Muhammad, the DC Snipers, killed random victims, often at gas stations, shooting them and leaving the scenes unnoticed.[33] In one of his letters to San Francisco Bay Area newspapers, the Zodiac Killer wrote "[killing] gives me the most thrilling experience it is even better than getting your rocks off with a girl".

Comfort

Material gain and a comfortable lifestyle are the primary motives of comfort killers. Usually, the victims are family members and close acquaintances. After a murder, a comfort killer will usually wait for a period of time before killing again to allow any suspicions by family or authorities to subside. Poison, most notably arsenic, is often used to kill victims. Female serial killers are often comfort killers, although not all comfort killers are female. Dorothea Puente killed her tenants for their Social Security checks and buried them in the backyard of her home. H. H. Holmes killed for insurance and business profits.

Power/control

Their main objective for killing is to gain and exert power over their victim. Such killers are sometimes abused as children, leaving them with feelings of powerlessness and inadequacy as adults. Many power/control-motivated killers sexually abuse their victims, but they differ from hedonistic killers in that rape is not motivated by lust but as simply another form of dominating the victim.] Ted Bundy traveled around the United States seeking women to control.

It's the same answer for what creates a bipolar or boarderline; paranoid or psychotic. It is a question of equifinality (the same things lead to a person being a serial killer) or multifinality (many different factors contribute to a person becoming a serial killer). Some serial killers are empathic, some never experimented with killing or torturing small animals. Some never see their prey, some purpetually "apologize" in some way for killing their victims. Because there are so many "types" and "sub-types" of serial killers, we can rule out a single-formula for creating a person who repeatedly kills others. So, there are multiple factors: biological, experiential, cognitive and emotional. In other words: NO ONE KNOWS. We can only determine forensically, one at a time, serial killer by serial killer.

I think they are all psychopaths (no cognitive awareness of right and wrong) who went over the edge when they discovered that they thrill at the kill. So, its their biology and their experiences.

I think a whole range of factors play a part in regards to becoming a serial killer.
Though if as a child a person finds great pleasure in killing insects, mice, setting fires, seems to have no sense of empathy for his or her peers, well then I think it is safe to say that a killer may just be itching to emerge.

A lack of empathy?

First, Kudos to ElLagarto, I almost spit out my soda all over my keyboard.

oddly enough, there is a theory that the forces that create police, firefighters, and soldiers are the same exact environmental triggers which create serial killers, arsonists, and gangsters/terrorists. The difference is how those factors are assimilated into the mind, and the specific surroundings of the individual- their ability to interact with those triggers.

Doubt it's as simple as this but i've read that there is a sort of recipe aspect to this, as they all share similar characteristics and life experiences. Apparently, there are three things in common most serial killers share in their past; 1) arson; they all tend to be fire-bugs as kids. 2)cruelty or torture or dissection of animals. 3)bedwetting and (very important) being ridiculed or punished severely by carers. Add to that an abusive, neglectful or traumatic childhood, psychopathy and in a lot of cases sadism, either sexual or otherwise & that's a rough recipe for a very dangerous predator. All killers are different in their choice of victim, modus operandi & preferred means of disposal, but apparently, they all share these three things in common, like an unholy trinity, if you will; arson, animal torture and bedwetting. Not sure why this is but i bet it's the key to finding what actually creates these monsters.

Mostly circumstance, imho. Bad childhood, perhaps. Unstable psyche, crushed dreams. I don't know. Probably many individual reasons.

I watched a documentary about this some time ago. The conclusion was that the one thing serial killers had in common seemed to be a sense that they were intellectually superior to other human beings. To them, the lives they had taken were inferior to them so not of importance.

They have little fear of getting caught because they believe they are too clever for that. Very often serial killers turn out not to hold much authority or status in their every day lives and so you can imagine that there may be a sense of anger and resentment that they are ruled by those they feel are beneath them intellectually.

Maybe to kill and get away with it gives them a sense of power and revenge. It also probably doesn't help that the press tend to give them nicknames and that may well give the killer a warbed sense of "celebrity".

People that commit this sort of crime have no empathy or sympathy for their victims or the families they destroy.

Opportunity and a blatent disregard for social norms

A person who let's their anger overwhelm their logic, unless they are really smart and can get away with it.

I think its a nice little combination of extreme paranoia, extreme narccissim, and outright hatred all rolled into a ball and directed at some poor misfortunate soul. Most s.k.s start at about age 6, by burning everything in sight. They get a power trip from starting fires. And they like to kill animals, especially cats. Because while they're killing them, they can feel alot of power over something helpless. I think that's the only way they know how to express their rage. I think they're very paranoid because they feel like everyone is mean, spiteful, and vicious because that's all they've ever been around, or that's all they see. Pretty much, I think that they are born with a chemical imbalance (psychopath), and society makes it a thousand times worse.

Upbringing & genetics.

Perhaps an obsession or focal point misdirected....

well you can look at this several ways
there have been many great writers who have created serial killers....like dr jekyll and mr hyde...freddie kruger

then there are tv shows that absolutely kill the concept of a good serial like 'lost' now there is a real serial killer

then there is your real life serial killer well they are power trippers .....i dont know whether it is the thrill of the kill or the power and cleverness they feel by getting away with it...probably both
a very sick and twisted mind creates a serial killer

I believe all criminals are 'not right in the head'... I hesitate to just label them as 'crazy' or 'insane' because that would sound like an excuse for the awful crimes that they commit. But people who murder for fun, for pleasure, are sick of mind and spirit; we all wish we lived in a utopian world, but when you hear about people that kill for the fun of it, you understand why we need policemen, prison guards and jail cells. They are extremely dangerous - but I don't know if it's faulty genes or a malevolent spirit that guides these types to commit such violent acts. Even science cannot fully explain the criminal mind.

I think eating Kellogs corn flakes cereal makes one into a cereal killer. I know that when I am forced to eat them I want to go strangle someone. I think that after a big bowl of corn flakes the guy runs out and shoots . . . . Oh, serial, I thought it was cereal. Sorry.

a mixture of bio and environment well hell they are just nutty buddies ....

i think its someone who grows up with an unbalanced home life- then they grow up pretty screwed up maybe hating women because their mother left a bad impression on them