There are criminals who use Satanism to justify their deeds, but they're few and far between. Murders have been committed in the name of Satan. Some criminals have latched onto the idea of Satan spurring them to kill and approving of their actions. And mental illnesses like schizophrenia have caused some people to hear voices that they attribute to Satan.
Richard Ramirez, the so-called "Night Stalker" who terrorized California in the mid-1980s, scrawled Satanic symbols and yelled Satanic slogans while committing his murders and during court appearances. David Berkowitz, aka the Son of Sam, claimed a demon (though not literally Satan) commanded him to kill people. Germans Manuela and Daniel Ruda, American teen Ricky Kasso and a heavy metal group called Hatred all committed gruesome murders while invoking the name of Satan.
There is one disturbing case in which a small cult named the Chicago Ripper Crew carried out a series of murders as part of Satanic rituals. In the early 1980s, four men kidnapped women and took them to their Satanic chamber (a rented hotel room), where they raped and murdered the women, and amputated one of their breasts. Their ringleader, Robin Gecht, was reportedly an avid reader of "The Satanic Bible." But these murders stopped once the perpetrators were arrested, and the perpetrators didn't seem to be connected to any kind of broad Satanist hierarchy that would continue the work [source: Johnson].
Members of black metal bands, like Varg Vikernes and Euronymous, burned down churches and committed at least one murder in the 1980s and 1990s. These crimes are often associated with Satanism, and the bands involved used Satanic imagery in their image and lyrics. However, it's more accurate to say that these crimes were specifically anti-Christian, and more closely connected to neo-pagan and far-right nationalist beliefs than ritualized, theistic Satanism [source: Sigel].
Almost every murder case with a reported Satanic influence was an isolated case of mental illness or an impulsive act intended to terrorize victims. These isolated "Satanic" murders are certainly terrifying, though, so it's understandable that America was swept into the Satanic Panic of the 1980s. And it's no surprise that movies and novels about murderous Satanists have been popular.