Most people use Facebook to connect with family and friends or to build professional connections. But a few use the social network in far more sinister ways. Facebook has occasionally become entangled with crime -- as a way to attract victims, as a place to broadcast villainous conquests, sometimes even by spurring a killer to action.
The disturbing interplay is common enough that it now has a name: "Facebook murder."
But not all Facebook murderers operate the same way. New research, published in the Howard Journal of Criminal Justice, looked at how the social network played into cases of Facebook murder from around the world.
Led by Elizabeth Yardley, a criminologist at Birmingham City University in the United Kingdom, researchers identified 48 cases of homicide between 2008 and 2013 in which the media had pointed to Facebook as having played a significant role. They analyzed the facts of the cases and divided the perpetrators into six distinct categories of Facebook killer.
One example it examined was that of a British man, Wayne Forrester, who killed his wife in 2008 after reading Facebook posts in which she announced the couple had separated and she wanted to meet other men.
The first type, called a reactor, is someone who reacts to content posted on Facebook by attacking the victim in real life, either right after viewing the post that makes them angry or following a certain period of time during which they revisit the post and analyze what it means. Forrester's case fits in that category.
Another type, called an informer, uses Facebook to let others know that they intend to kill the victim or that they have killed them. Killers classified as informers use social media to demonstrate their control over the victim.
The type of killer called an antagonist participates in hostile exchanges on Facebook that eventually turn into offline, real-life fatal violence. Killers in the antagonist category may arm themselves with weapons as the conflict escalates.
Fantasists use Facebook to perform or maintain a fantasy or prevent others from discovering their lies. The researchers say that for fantasists, the line between their fantasy life and reality may become increasingly blurred, and they may kill to stop someone from exposing them.
Predators come up with and maintain fake profiles to attract victims and meet them offline. Killers in this category may use information on the victim's profile to identify and exploit weaknesses, and to help them develop a relationship with the victim. The study cited an example from Australia in 2010, when a man named Christopher Dannevig pretended to share a young woman's love of animals online and lured her to meet him at a nature preserve, where she was killed.
The last type, the impostor, is someone who posts disguised as someone else to access and monitor a planned victim's profile. After the murder, this type may also pose as the victim online to create the illusion that he or she is still alive.
But despite the role that Facebook and other social networking sites have inadvertently played in some disturbing crime scenarios, Yardley stressed that the sites themselves should not be blamed.
"There is nothing inherently bad about them," she said. "Facebook is no more to blame for these homicides than a knife is to blame for a stabbing -- it's the intentions of the people using these tools that we need to focus upon."
She also said that a goal of the research was "to see whether homicides in which Facebook was reported to have been involved were any different to other homicides and found that on the whole they are not."