As any frequent listener of audiobooks will know, a narrator’s voice can either make or break a book. It’s the equivalent of listening to the dulcet tones of David Attenborough or the nasal drag of Janice from Friends. But aside from the story itself, these kind of shallow aesthetics are often all that listeners stop to think about. How many of you can honestly say that you’ve ever paid attention to the voice behind the story? Well, the revelation that a particularly infamous serial killer has been moonlighting, from prison, as an audiobook narrator might make you pay more attention.

If you’ve ever watched Netflix’s crime-drama Mindhunter, then the name Ed Kemper is probably familiar to you already. If not, let’s briefly recap. In the 1970s, Kemper abducted and murdered six young female hitchhikers, having previously been detained in a psychiatric hospital for killing his grandparents almost a decade earlier. His final victims were his mother’s best friend and his own mother, whom he considered to be emotionally abusive. Kemper killed his mother in her sleep before dismembering her, using her head as a dartboard and engaging in necrophilia with her corpse. Later, he called the police to facilitate his own arrest.

As it turns out though, the 6"9 tall and 250lb murderer, also has a softer side. After receiving eight life sentences for his crimes - a judge having refused his request for "death by torture" - Kemper was transferred to the California Medical Facility, where he began recording audiobooks for the blind. Part of a programme known as Volunteers of Vacaville, he began the process in 1977, just four years after his incarceration, and by 1987 had become its most prolific volunteer. Perhaps it was inevitable that Kemper would need something to occupy himself, because in addition to being known as a macabre serial killer, he is also noted for being highly intelligent, with a reported IQ of 145. For context, the average person's IQ sits at somewhere between 70 and 130.

Although Kemper is no longer featured on the Volunteers of Vacaville members list, to date he has recorded over 100 audiobooks and clocked up over 5000 hours in the recording booth, apparently with penitence at the forefront of his mind: "I can't begin to tell you what this has meant to me, to be able to do something constructive for someone else, to be appreciated by so many people, the good feeling it gives me after what I have done," he told the Los Angeles Times in 1987.

So what literary classics has this infamous killer lent his voice to? Well, of the small selection listed on a now defunct website established for the audiobook project, there are a selection of feisty westerns, slushy romances and - somewhat ironically - a selection of horror and detective stories, including Flowers in the Attic, a Gothic horror novel by V. C. Andrews, focuses on the subjects of an evil grandmother and incest. A recording of the novelisation of the Star Wars trilogy is also credited to Kemper.

Concerning as Kemper's choice of literature may be, it seems that his efforts were well received by listeners: "These prisoners are doing so much for the unseeing population. We just wanted to come here, to meet them and to thank them personally for their dedication to a program that means so much to the blind," Toni Ann Gardiner and Ed Eames, two audiobook recipients told the Los Angeles Times during a visit to the prison.

Audiobooks weren't Kemper's only good deed while in prison either, as is portrayed in Mindhunter. He really did spend time helping the FBI develop their criminal profiling systems. Since Kemper's recording career has apparently finished, he has found other ways to occupy his time - reputedly indulging in crafting ceramic pottery - and is now said to be considered a model inmate by prison staff. Apparently content with his life in prison, he has repeatedly waived the right to his parole hearings.

According to a 2017 report on the Volunteers of Vacaville, part of their current aim is to convert cassette recordings of Kemper and other narrators into digital formats for their future use. So, while we don't mean to ruin your enjoyment next time you sit down with a cup of tea and zone into favourite audiobook, lulled by the smooth, smokey voice working its way into your ears, take a second to think about who that voice belongs to - it might just be "America’s most charming maniac". And if you use audiobooks to fall asleep at night, sleep tight!