María del Pilar Pérez López was born on December 21, 1951, in Providencia, a district in Santiago, Chile. She was the eldest daughter of José Pérez Pérez, a Spanish immigrant who operated a successful bakery, and María Aurelia López Castaño, an Argentine woman known for her strict, authoritarian personality. Pilar grew up with two younger sisters, Gloria and Magdalena. According to family testimonies and reports from the investigation, she displayed behavioral issues from a young age, including anger outbursts and early incidents of theft.

Pilar later studied and worked as an architect. On March 3, 1976, at the age of 26, she married Francisco Pelayo Elías Zamorano Marfull, with whom she had two children: Juan José and María Rocío. Over the years, her marriage deteriorated, particularly after Francisco revealed his homosexuality and separated from her. This created significant tensions within the family, especially surrounding the future of her father's business and inheritance.

Her father, who began suffering from Alzheimer’s disease during the 1990s, initially wished to pass the family bakery to Zamorano, but changed his mind following the separation. Upon his death, Pilar inherited a significant portion of his estate, including the Seminario 95 and 97 properties in Providencia. Over time, Pilar was described by relatives as increasingly violent, and her behavior became erratic. In July 2007, she physically assaulted her daughter-in-law, Montserrat Hernando Berríos. Family members, including her own mother, later described Pilar as manipulative and obsessed with control and wealth. She had even joked about how easy it was to hire hitmen in the United States after a trip to New York.

In 2008, María del Pilar Pérez López orchestrated a series of murders that shocked the nation. Using funds from her father's inheritance, she hired José Mario Ruz Rodríguez, a known criminal, as a hitman. She provided Ruz with detailed information, including maps of her victims' homes, marked with the locations of bedrooms and valuables.

The first killings occurred on July 23, 2008, when Ruz fatally shot Pilar's ex-husband Francisco Zamorano Marfull and his partner, Héctor Rodrigo Arévalo Olivero, in their home on Seminario Street. Just a few months later, on November 23, 2008, Ruz attempted to carry out a second attack, this time targeting Pilar’s own extended family. The goal was to eliminate everyone in the household and secure the rest of her father’s inheritance. However, Ruz only managed to shoot and kill 23-year-old Diego Schmidt-Hebbel Niehaus, who was dating Pilar’s niece, before being discovered and fleeing the scene.

The investigation moved quickly. A witness recorded Ruz’s license plate, leading to his arrest within weeks. Under pressure, Ruz confessed to the crimes and implicated Pilar as the mastermind. Soon after her arrest, Pilar attempted suicide and wrote a letter to her daughter asking her to bribe Ruz to change his story and blame another family member. Her manipulation, however, failed.

Her trial began on September 23, 2010, and became one of the most high-profile court cases in Chile. Over 100 witnesses and 60 pieces of evidence were presented. Prosecutors charged her with multiple crimes: parricide, qualified homicide, robbery with homicide, and four attempted murders—including attempts on her niece, her mother, her sister, and her sister’s husband. Despite her plea of innocence, she was convicted on January 19, 2011, and sentenced to life in prison with no chance of parole for 40 years. José Ruz received the same sentence.

Her former home, Seminario 95, caught fire in 2012 and was eventually sold to compensate the victims' families. The neighboring home, where Schmidt-Hebbel was murdered, was demolished and replaced with businesses.

Pérez is currently serving her sentence at the San Joaquín Women’s Prison. She has reportedly clashed with other inmates, including convicted murderer Jeannette Hernandez, and was part of the organizing committee during Pope Francis’ 2018 prison visit. In 2022, she launched a YouTube channel with her lawyer called “Pilar’s Voice,” continuing to assert her innocence and seeking to have her conviction overturned. Her case inspired the 2023 Chilean crime series Alma Negra ("Black Soul").