"I actually can't imagine what was going through his mind," the angered author said.
The Transformers actor apologised in a series of tweets, admitting his guilt.
Copying isn't particularly creative work. Being inspired by someone else's idea to produce something new and different IS creative work.
In my excitement and naiveté as an amateur filmmaker, I got lost in the creative process and neglected to follow proper accreditation
Im embarrassed that I failed to credit @danielclowes for his original graphic novella Justin M. Damiano, which served as my inspiration
I was truly moved by his piece of work & I knew that it would make a poignant & relevant short. I apologize to all who assumed I wrote it.
I deeply regret the manner in which these events have unfolded and want @danielclowes to know that I have a great respect for his work
LaBeouf closed his apology with a simple, "I f***** up".
Interestingly, BuzzFeed have noted that LaBeouf's Twitter apology closely resembles a message posted four years ago on Yahoo! Answers by a user named Lili.
In response to a question, 'Why did Picasso say "good artists copy but great artists steal"?', Lili's answer reads: "Merely copying isn't particularly creative work, though it's useful as training and practice. Being inspired by someone else's idea to produce something new and different IS creative work."
This is not the first time the actor has been accused of plagiarism, after he took blocks of quotes from Tom Chiarella's Esquire article, What Is A Man? and copied them into an email he sent to 30 Rock star Alec Baldwin after a spat.
Shia LaBeouf has recently finished filming for Lars von Trier's controversially explicit movie Nymphomaniac.
It will debut in Copenhagen on Christmas Day before a likely general UK release in March 2014.
The film's raunchy poster campaign, also directed by Danish director von Trier, shocked in October with its images of the cast pretending to reach sexual climax.
Uma Thurman and Jamie Bell are among the actors portraying orgasmic ecstasy to promote the film, which follows the erotic life of a woman from birth to the age of 50.
- Independent