The movie The Avenging Conscience (1914), also titled ‘Thou Shalt Not Kill’, is a silent horror film directed by D. W. Griffith. The film is based on Edgar Allan Poe’s 1843 short story “The Tell-Tale Heart” and his 1849 poem “Annabel Lee”. It is sometimes considered the first full-length feature horror film.
In The Avenging Conscience (1914), a young man (Henry B. Walthall) interested in the works of Edgar Allan Poe, falls in love with a beautiful woman (Blanche Sweet), but he is prevented by the uncle (Spottiswoode Aitken) that raised him since childhood from pursuing her. Tormented by visions of death and suffering and deciding that murder is the way of things, the young man kills his uncle and builds a wall to hide the body. The young man’s torment continues, this time caused by guilt over murdering his uncle that was overheard by an Italian witness, and he becomes sensitive to slight noises, like the tapping of a shoe or the crying of a bird. The ghost of his uncle begins appearing to him and, as he gradually loses his grip on reality, the police figure out what he has done and chase him down. In the ending sequence, we learn that the experience was all a dream and that his uncle is really alive. They make up, and the nephew gets to marry the sweetheart. 
- Henry B. Walthall as the nephew
- Blanche Sweet as his sweetheart
- Spottiswoode Aitken as the uncle
- George Siegmann as the Italian
- Ralph Lewis as the detective
- Mae Marsh as the maid
The movie The Avenging Conscience (1914) had a massive influence on young Alfred Hitchcock.
“Conscience is a good film to discuss on the 210th anniversary of the birth of Edgar Allan Poe because it plays like fan fiction of that author’s works.” 
“I’ll stop short of calling this feature a full-fledged horror film. In 1914, of course, there was no established tradition of horror films as we know them today (Edison’s 1910 production of Frankenstein notwithstanding). The Avenging Conscience is something more quirkily personal than that anyway” 
“Director D.W. Griffith offers up an interesting tale with some groundbreaking visuals. Interesting that just one year later, Griffith would direct what is still one of the most controversial films ever made, The Birth of a Nation.”