Efraín Sarmiento Cuero was born on May 20, 1996, in Policarpa, a small town in the Nariño department of Colombia.

Efraín Sarmiento Cuero is known for committing a series of violent acts against women. His first known victim was Cristiana Mendoza Maya. In April 2017, they were together in a hotel in Cali, Valle del Cauca. Mendoza's body was found by hotel staff. She had been raped, strangled, and beaten before her death.

In November 2018, he killed another woman named Jacqueline Muñoz Ojeda. They were at a hotel in Pasto, Nariño. After a fight, Sarmiento assaulted her and then used a belt to strangle her. He was arrested soon after and linked to both murders. He was tried and found guilty of these crimes, receiving significant prison sentences for each.

After his convictions, Sarmiento was moved to El Barne Prison in Cómbita, Boyacá. While in prison, he met Merly Andrea Rengifo Cuadros online. They started a relationship, and Rengifo visited him regularly. Sarmiento became controlling and demanded constant updates about her whereabouts.

On May 14, 2023, during a visit from Rengifo on Mother’s Day, they had an argument. In the heat of the moment, Sarmiento grabbed a shiv and cut her throat. When prison staff found Rengifo, she had multiple bruises on her body. Sarmiento later stated he did this to show that she was "his."

Following this murder, authorities noted that Sarmiento was too dangerous to remain with other inmates. He was charged with femicide and is now awaiting trial for this crime.