Pedro Alonso López was born on October 8, 1948, in Venadillo, Tolima, Colombia. He was the seventh of thirteen children in his family. His mother, Benilda López de Castañeda, worked in a laundry. Pedro claimed that she was a sex worker, which contributed to a difficult childhood. His father, Megdardo Reyes, was murdered during a violent period in Colombia known as La Violencia, just six months before Pedro was born. This left Pedro growing up without a father.

At the age of eight, he was banished from his home after his mother caught him trying to molest his sister. After being kicked out, he became homeless and wandered the streets of Bogotá. During this time, he faced frequent sexual abuse from others. To feel safer, he joined a gang of street children.

When he was twelve years old, an American immigrant family adopted him. Sadly, this situation did not last long. Pedro ran away from the family after he was sexually assaulted by a teacher. In 1969, he got into trouble with the law and was sentenced to seven years in prison for auto theft. While in prison, he suffered further abuse and ultimately killed three inmates who had raped him, which extended his sentence by two more years.

Upon his release from prison in 1978, Pedro Alonso López wandered throughout northwestern South America, eventually arriving in Peru. He claimed to have killed over 100 girls during this time, focusing on street children from indigenous tribes. One notable incident involved López attempting to abduct a 9-year-old girl, which led to his capture by an Ayacuchoan indigenous tribe. They stripped him and buried him in sand. An American missionary persuaded the tribe to release him to the police, but the police did not detain him. Instead, he was expelled from Peru.

After being deported, López continued his killing spree. Authorities noticed an increase in missing persons, especially young girls, but attributed the disappearances to human trafficking. In April 1980, heavy flooding in Ambato, Ecuador, uncovered the remains of several young girls who had been reported missing. This discovery prompted police to revisit their investigations, which eventually led to López's arrest later that year.

A local woman named Carvina Poveda was heading to the market with her daughter when López attempted to abduct the girl. Local merchants subdued him until the police arrived. While in custody, López initially refused to talk, but later began confessing his crimes to a police captain who had pretended to be a fellow inmate. He claimed to have murdered more than 200 individuals in Ecuador, along with additional victims in Peru and Colombia. López explained his method of luring victims before attacking them and mentioned that he would sometimes dig up the bodies for "tea parties." He attributed his actions to his loss of innocence at a young age. Following his confessions, he guided authorities to the remains of 53 victims, confirming a total of 110 murders in Ecuador.

López was convicted of murder in 1980 and received a 16-year prison sentence, the maximum at that time. He served two years of his sentence before being released early in 1994. After his release, he was deported to Colombia, where he was detained as an illegal immigrant. Colombian authorities declared him insane and committed him to a mental hospital. In 1998, he was deemed sane and released on bail but soon disappeared.

The last known sighting of López was in September 1999 when he attempted to renew his citizenship card. In 2002, Colombian authorities issued warrants for his arrest related to a murder that resembled his previous crimes. An Interpol warrant was deactivated in 2005, but he remains a fugitive and has been linked to other potential homicides.