How do you define a writer whose chief game plan was to escape definition? Today that seems almost the only true way to pin down Truman Capote: by calling him un-pinnable.

What on earth was he? Who was this mincing prince of New York high society who became a gritty nonfiction novelist? Who was this loving fantasist of the demimonde who became, with his last, unfinished novel Answered Prayers — an epic project based on the lives and characters of his friends (some of whom soon became non-friends) — an acid-spitting diarist, a poison-tipped Proust?

“Let’s write about Capote and the movies.” When my editor said that — to chime with the release of Ebs Burnough’s The Capote Tapes, a new bio-doc on the author — I seized the idea; though I felt it should have arrived like one of those “Come to dinner” invitations received by imminent victims in an Agatha Christie murder story. What death — or fate worse — was waiting? What wrestlings with the unknowable? Capote himself played the host of such a killing party in his only notable film role. Superintending the demises of a starry cast in Murder By Death (1976), he is gleefully self-parodic — a plump, primping, pink-suited elf, fluting campy menace.

The two best-known films based on his books are a spectacularly contrasting pair. Breakfast at Tiffany’s is a bittersweet romcom in bright pastels, based more than loosely on his novella about a New York good-time girl. For the book: imagine Christopher Isherwood’s Goodbye to Berlin (Cabaret to be) with Sally Bowles replaced by Holly Golightly, a Boho, scattily tempestuous hooker who is in part, surely, a self-portrait of the writer: Capote in his young-nymph days as a gay darling and aspiring courtesan of the Manhattan culture. (The youthful photos and footage of young Truman in The Capote Tapes attest to his extraordinary mix of fey beauty and scary, confrontational intensity of gaze.) For the 1961 film: imagine — or watch — a series of Givenchy dress tests for Audrey Hepburn, set that to Henry “Moon River” Mancini’s music. Blake Edwards’ screen adaptation has charm in a wispy-wistful, candyfloss way. And it has a romance, which the original definitely doesn’t.

In Cold Blood, the book, helped to form the big-fiction empire of New Journalism. It brought a novelist’s art and density to a true story. A multiple killing in a Kansas farmhouse, and the investigation and trial following, are reconstructed with an epic thoroughness, at once forensic and imaginative.

Richard Brooks’s In Cold Blood (1967) is a better film than Breakfast at Tiffany’s. But it still misses the essential allure of the novel. Which is? Again that Capote is there, invisibly; that the insistent question in the reader’s mind is “What exactly is the author’s interest in, and relationship with (actual or wished-for), with these two killers?”

Some speculate that the author was romantically obsessed with one of them. It’s an area expertly explored by The Capote Tapes — “He was really in love with Perry [Smith],” insists a friend — which trawls every lost interview or untapped interviewee to get at the Truman essence. In the same film, other familiars of the writer, including his friend from childhood Harper Lee (who wrote a Capote cameo into To Kill a Mockingbird, sketching him as the skittish, rambunctious boy next door), remember that the author was desperate for Perry and his fellow killer to have their delayed deaths in the electric chair. What closure, otherwise, for an unpublished and keenly awaited book? “Why are they torturing me?” wails Philip Seymour Hoffman in the title role of Capote (2005) at the continual stayings of execution.

The two dramatised films about Truman Capote, rather than those based on his work, are more successful in getting the measure of his capricious genius. Both Bennett Miller’s Capote, scripted by Dan Futterman, and Doug McGrath’s Infamous (2006), with Toby Jones a physical and vocal dead ringer for TC, put the author at the centre of his own world, real and imagined, with lines blurring between fact, fiction and factoid.

Capote World — what else to call it? — is a place worthy of a Disney-style theme park for grown-ups. The hottest property in Hollywood among Capote’s late works was Handcarved Coffins (1980). A brutal, bleakly brilliant gothic detective story, it pretends to be a “nonfiction” yarn in the In Cold Blood genre, with its multiple-murder investigation in a Southern town. But no reader or researcher has discovered any basis in truth. As with the Coens’ film Fargo, the reality premise may be a put-on. Teasingly, though, Capote is there throughout the tale as first-person narrator and reporter.

Handcarved Coffins never became a movie but was pursued by notable directors, including Michael Cimino. With a career in crisis after Heaven’s Gate (1980), Cimino must have seen the material for a miniaturist masterwork, the opportunity for a comeback at once crystalline and powerful. All Capote’s gifts are there on the page: poise and poison; gossip and gallows wit; the disrobing of lies. At the story’s end, with its initially frustrating withholding of a murder-case resolution, comes a sly, magnificent twinning of evils: serial homicide and the coercive preyings of evangelical religion.

The Capote oeuvre never became a major mother lode for movies. Too much mischievous elusiveness; too much untranslatable interplay between seer and subject. Capote himself, though, dabbled in screenwriting. Beat the Devil (1953) was a louche caper flick co-scripted with director John Huston. The Innocents (1961) was a skilful Henry James adaptation. The Great Gatsby (1974) was re-scripted by Francis Ford Coppola after Paramount deemed Capote’s version unusable. The author also bequeathed his autobiographical novel The Grass Harp to the Southern whimsy industry, school of Steel Magnolias and Crimes of the Heart.

Best, perhaps, to muse on what might have been. Or what might still be — if a true Capote believer can take Breakfast at Tiffany’s (again) or Handcarved Coffins or any of his creepily hypnotic late tales and give us a Truman show worthy of the name and the numinous, luminous potential.

‘The Capote Tapes’ will be available at altitude.film and on digital platforms from January 29