“Friends are our connection to this world,” says Lionel Dahmer, concerned by the fact that his eldest son, Jeffrey, doesn’t seem to have any. Yet, as this film’s title suggests, Jeffrey Dahmer had at least one friend – John “Derf” Backderf, who wrote the bestselling, based-on-a-true-story graphic novel it’s adapted from.

Jeffrey Dahmer would go on to become one of America’s most notorious serial killers, raping, murdering and cannibalising 17 young men, and confessing to his crimes in 1991. In this drama, writer-director Marc Meyers looks at Dahmer in his last year of high school in an attempt to figure out who he might have been before the atrocities that came to define him.

In 1978, among the verdant forests of Bath, Ohio, Dahmer (Ross Lynch) collects roadkill, dissolving it in acid in a shed at the back of his garden. Dead cats; stiff, bloodied possums; unidentifiable animal corpses bottled in formaldehyde – he “likes” bones. “It interests me, what’s inside,” he mutters, palming dried bones as though they were worry beads. Chastised for his unsavoury after-school activities by his chemist father Lionel (Dallas Roberts), and butting heads with his erratic, depressed mother Joyce (Anne Heche – a little hammy here) at home, Dahmer also acts out in the classroom. Imitating an aggressive epileptic seizure, he becomes a source of fascination for a prankish group of boys including aspiring artist Derf (Alex Wolff of Nickelodeon show The Naked Brothers Band, and the forthcoming Hereditary). Interpreting his “spaz” attacks as a form of countercultural resistance, Derf and friends form the “Dahmer Fan Club”, putting him in the background of every school yearbook photo and encouraging him to continue this “performance art” in other public spaces.

Meyers makes the most of the 70s setting, from Dahmer’s aviator glasses to the saturated gold-browns of Daniel Katz’s widescreen cinematography and the creeping hangover of the liberal excess that thrived in the previous decade, prior to Reagan’s America. He also makes the most of Lynch, a Disney Channel kid best known for his role on the TV series Austin & Ally, and in the teen boyband R5. With a shock of blond hair that flops over his eyes, shuffling feet and a hunched, lumbering gait, Lynch’s performance is remarkably physical, internalising the way shame weighs down on the character’s shoulders. He doesn’t walk so much as stalk, his body dragging behind him as he slips further inside himself. There are glimmers of the icy charm that perhaps helped him seduce his victims – like in a scene where he persuades a younger female classmate to go to prom with him.

Yet Dahmer isn’t really interested in women. He develops a crush, if you could call it that, on a male jogger who turns out to be a neighbouring doctor (Vincent Kartheiser), and wrangles a physical examination with “Dr Matthews”. The film’s single most interesting sequence sees Dahmer masturbating, his back to the camera, following their otherwise innocent encounter, convulsing in humiliation that quickly turns violent – and morbid. It would be troubling, lazy pop psychology to draw a straight line between Dahmer’s closeted homosexuality and his vicious impulses, but Lynch’s acting complicates this subplot. It’s not just the embarrassment of rejection that he captures but a clue – a kind of spark of recognition – about his sexuality, swiftly disregarded.

“He’s not a sideshow attraction,” insists one of Dahmer’s friends, and Meyers tries his best not to treat him as such. Unlike the source material (a memoir written from Derf’s perspective), the film operates from a conventional, omniscient point of view, allowing the audience to experience Dahmer’s private moments. At times, the film struggles to permeate his psyche. However, the way the character wobbles between bizarre high-school band kid and burgeoning psychopath works as an acknowledgement of Derf’s fallible memory – after all, the film is based on his recollections, not Dahmer’s. Derf’s impulse to fill in the gaps – sometimes too simplistically – in order to make sense of the crimes his friend would commit feels like a queasy admission of complicity.

It makes for something that ends up being sadder, weirder, more boring – but more convincing – than the average serial killer movie.