The Culture and Media Institute, a division of the Media Research Center, said a study found there were 35 percent more such shows on television this year than last, and called it a "major trend."
"Television is a copycat medium," said Dan Gainor, vice president of the Culture and Media Institute, which authored the analysis. "What happens first on cable migrates to broadcast TV. Everyone is trying to capture that Dexter audience."
"Dexter" -- about a police blood spatter pattern analyst who leads a secret, double life as a serial killer -- premiered in 2006 on Showtime.
There were seven new television shows about serial killers this year -- including "Hannibal," "Bates Motel," "The Cult," "The Bridge," "Ripper Street," "The Following" and "The Fall," The Hollywood Reporter said Friday.
The analysis made mention of a scientific poll conducted by The Hollywood Reporter in which 27 percent of viewers said shows like "Modern Family" and "Glee" made them feel more support for same-sex marriage.
"Hollywood is taking a victory lap on same-sex marriage, but will they take responsibility for 20 shows about serial killers next time some lunatic kills a dozen people at a school?" Gainor said. "No, they won't, because they're not that honest."