British "Grindr Killer" Stephen Port was convicted of killing several men and sentenced to life in prison in November 2016. (Credit: Courtesy of the Metropolitan Police)

The paraphilia of a British serial killer may be a relatively new phenomenon that investigators should keep an eye out for among rape and murder cases, according to a new study in the Journal of Forensic Sciences.

Stephen Port, known as the “Grindr Killer” killed four men and perhaps many more; the investigation into 58 other deaths continues to this day. He was convicted and sentenced to life in prison in November 2016.

Port’s modus operandi was to lure men to his home for sex through the app Grindr and other networks. He would then administer gammahydroxybutrate (GHB) through a glass of wine, or through direct anal administration, before raping them. The four confirmed victims who died in 2014 and 2015 essentially overdosed on the drug.

Port video recorded some of the rapes. He didn’t stop the cameras even after one victim had died.

But the deaths were incidental to his drive to satisfy his paraphilia, according to the new paper, by Mark Pettigrew of Leeds Beckett University.

The Grindr Killer is a somnophile—a paraphilia in which arousal is derived from violating a sleeping person. That makes it different from a date rapist’s attack, where the sexual act is paramount, not necessarily the state of the victim, according to the study.

“The case of Stephen Port is distinct from those cases of date rape where a perpetrator surreptitiously administers a substance to a victim in order to take advantage of them,” writes Pettigrew. “Stephen Port was aroused by passivity; he was attracted to the unconscious state of this victims, their inability to resist his sexual advances, whereas the more common date rapist is aroused by the sexual act and unconsciousness is simply the means by which it is facilitated.”

Not all the victims died. Several later said they could not be sure of the extent of the sexual activity after the attack.

But at Port’s trial, the jury was shown an 18-minute homemade video of the killer raping an unconscious man.

In one instance, even after the death of a victim, Port continued to experiment with the administration of drugs—and recorded a necrophilic rape, according to the paper.

The death toll attributed to Port could continue to grow. Even now the London Metropolitan Police are looking into 58 further GHB overdose deaths.

The police investigation has been called into question.

Indeed, Port’s first known victim was dumped outside the flat of the killer, who called anonymously to report a young male that was drunk or had "collapsed." Port was not arrested, and escaped detection for months afterward, according to press accounts.

Ten police officers have been served misconduct notes, with another seven served with gross misconduct notices for the suspicion of homophobia, which prevented the linking of the cases earlier in the investigation.

But all death investigators should keep an eye out for the fetishists who seek out sleeping targets—no matter their modus operandi, according to the paper. The Diagnostic Manual of Mental Disorders’ fifth edition (DSM-5) defines a paraphilic disorder as one in which a person’s sexual desire causes another’s distress, injury or death. In Port’s case, all three were achieved—and he kept counting victims.

“The limited knowledge base on somnophilia would benefit from further research and study of those who are attracted to the sleeping and unconscious object in order to try and identify and refine appropriate treatments and interventions,” writes Pettigrew.