Diego Alexánder Ruiz Restrepo was born on March 14, 1990, in Cali, Colombia. His mother became pregnant when she was only 16 years old. The father of Diego left when he learned of the pregnancy. Because of this, Diego was raised by his maternal grandparents. He attended the Colegio Carlos Holmes Trujillo in the Aguablanca District of Cali.

Diego worked as a car mechanic for five years, which was his longest job. In 2010, his mother moved to Chile. Diego followed his mother three years later, entering the country by pretending to be a tourist. In Chile, he worked in various jobs, mostly in civil construction.

At the age of 22, Diego became a Christian, like many in his family. He was known for being well-liked in his neighborhood back in Cali. During his time in Chile, he had a son named Andy. Andy was born from Diego's relationship with an Ecuadorian woman.

Starting in 2015, Diego lived in an apartment with his sister and her husband in the Santiago commune of La Alameda. However, his brother-in-law described him as someone who struggled with alcohol and had a violent and abusive behavior towards his sister. At some point, he stabbed several family members, including his sister, his mother, and his grandfather. As a result, his sister obtained a restraining order against him.

Diego was also involved in conflicts in his neighborhood. He had a history of getting into fights and threatening people with weapons. He had a police record that included charges for robbery, threats, and the use of bladed weapons. This history made it difficult for him to get a permanent residence visa in Chile.

Diego Alexánder Ruiz Restrepo's murder spree began on March 7, 2020, when he killed his first known victim, 72-year-old Víctor Olegario Allende Salas. Ruiz's next murders took place on November 1, 2020, when he killed Colombian immigrant Carlos Andrés Rivas Angulo, 35. Later that day, he also murdered 64-year-old Guido Hernán Gallardo Contreras, who was homeless.

On November 8, 2020, Ruiz committed four more murders in a single night. His first victim that night was 49-year-old Luis Marcelo Romero Jeria, also homeless. Following him was 57-year-old Marcia Margot Tapia Loncón, a woman who struggled with alcoholism and schizophrenia. Next, he killed 40-year-old Leónidas Vicente Panez Fierro, a former police officer who was living on the streets. The last victim, 32-year-old Rodrigo “Che” Manino Carmona was an Argentine immigrant.

On August 3, 2020, Ruiz threatened another individual, Óscar P., with a knife, claiming he had killed many before him. On November 8, 2020, he also attacked Pedro Manuel Bustamante Babbonney, who survived the attack.

Investigators linked Ruiz to at least 20 other deaths. They studied his behavior patterns and reviewed security camera footage that captured his movements. He was arrested on November 9, 2020, and charged with multiple murders. Over time, he became connected to several crimes beyond those confirmed.

By January 2021, he was in preventive detention. In July 2023, Ruiz was sentenced to life imprisonment, eligible for parole after 40 years. He primarily targeted homeless individuals, as they often went unnoticed by families. His deadliest night involved attacking five people in just 70 minutes, leading to four deaths.