During the Mexican Revolution, Archibaldo's indulgent mother gave him her special music box, which his stern governess said had the power to cause the death of one's enemies.

Admitting he liked how powerful this made him feel, Archibaldo threatens the nun with a straight razor, but she runs away, only to fall down an open elevator shaft.

An attractive woman named Lavinia and her elderly fiancé are looking at it, but Archibaldo convinces the salesman to sell it to him instead by saying it belonged to his mother and was stolen during the Revolution.

Outside the home of Carlota Cervantes, a young woman he is courting, Archibaldo runs into Patricia Terrazas, who recognizes him from a gambling parlor they both used to frequent.

While Patricia pours them drinks, Archibaldo imagines killing her and prepares to do it for real, but Willy enters, interrupting his plan.

Patricia admits she was just trying to make Willy jealous, and Archibaldo leaves when the couple begin to kiss, though they are already arguing by the time he walks out the door.

After Lavinia leaves with the tourists, Archibaldo takes the mannequin and puts it in his kiln, watching with a perverse glee as it melts.

Ensayo de un crimen has been analyzed and studied by academics and critics such as Victor Fuentes, Gerardo T. Cummings, Marsha Kinder, and Ilan Stavans.

Fuentes, a retired professor from the University of California, Santa Barbara, included chapters dedicated to the detailed analytical study of the film in his book, La mirada de Buñuel (Spain: Tabla Rasa Libros y Ediciones, 2006), finding correlations between Ensayo de un crimen and Él.

[2][3] In 2002, Slant Magazine called the film "a twisted tragicomedy on male obsession [...] the closest Spanish auteur Luis Buñuel ever came to directing a bona fide suspense thriller.

"[4] Buñuel briefly references the production of Ensayo de un crimen in his 1983 autobiography Mon dernier soupir (My Last Breath).

In it, he recounts how he was syndicated into orchestrating an original composition for the movie, and that, when the members of the orchestra disrobed due to heat, he saw that "at least 3/4ths of them carried holstered guns".