[2] Born in a family of Irish ancestry originally from Chascomús, by 1922 the Banks brothers owned two cattle ranches in Parish, a rural area several miles north of Azul, referred to as "El Trébol" ("The Shamrock") y "La Buena Suerte" ("The Good Luck").

[5] Mateo Banks lived away from the ranches in a luxurious house in the town, with his upper-class wife Máxima Gainza, three sons and a daughter.

[4] A fervent and charitable Catholic, he was a member of the local chapter of the Jockey Club Argentino, the vice honorary consul of the United Kingdom and the commercial representative of the Studebacker car company in the region.

[6] Azul's historians Georgina Degano and Eduardo Aguero Mielhuerry carried out a research on Mateo Banks early life, and discovered some evidence of a criminal past.

After improperly flirting with one of McCracken's daughters, Mateo Banks became involved in the theft of a sum of money from his employer (a couple also working in the ranch was accused and fired).

There were two more suspicious deaths by firearm at "La Buena Suerte"; the first, a visitor from Buenos Aires, shot dead in the course of a hunting trip in the ranch, and the second, one of Matthew's brothers.

[7] While living in San Luis, he married Máxima Gainza, the daughter of a rich Basque landowner from Olavarría, a town some miles away from Azul.

They drank mate with Banks, who shortly after paid a visit to his brothers Miguel and Dionisio at El Trébol and La Buena Suerte, where they lived with their families.

While staying with them he attempted to poison his relatives at lunchtime with strychnine in their puchero, but the bad smell and flavour resulted in the food being discarded.

[6] In the afternoon, when Banks realized that his plans of poisoning his family had failed,[9] he traveled by sulky from Los Pinos to La Buena Suerte, where his brother Dionisio was staying with his twelve-year-old daughter Sarita.

[3] At night he awoke his sister, convinced her to come to La Buena Suerte to check on Dionisio, and shot her in the back along the way, dropping her lifeless body from the sulky.

[11] In the course of the investigation it was revealed that Banks had lost his fortune to gambling[12] and was on the verge of destitution even after having sold part of his inheritance to his siblings.

[9] The prosecutor concluded that Banks wanted both to conceal his past misdeeds from the family and inherit the fortunes of both María Ana and Miguel.

At the second trial famed lawyer Antonio Palacios Zinny tried to garner sympathy with the jury by having Banks poisoning himself in front of them with a (non-fatal) dose of cyanide.