Juan Roa Sierra was unemployed, and people described him as a lazy dreamer and extremely quiet and reserved. He was living in the neighbourhood Ricaurte with his mother, who was his sole financial support and by all accounts was incredibly unremarkable. He himself thought he was destined to greatness, having dreams of treasures buried under indigenous villages and delusions of grandeur. Roa Sierra's mental health had also deteriorated to the point that he was convinced he was a reincarnation of Gonzalo Jiménez de Quesada and of Francisco de Paula Santander. He would even style his hair to resemble those historical figures and stare at his own image in the mirror for hours.

Roa Sierra went several times to the office of Gaitán, by all accounts Roa Sierra's disappointment in Gaitán after the latter refused to offer the former a job or any financial help and simply directed him to seek assistance from the government. Roa Sierra's last visit to Gaitán was on August 7. On this same date Roa Sierra purchased the weapon and the next day he bought the ammunition from a pair of unscrupulous young hooligans.

On August 9th, Roa Sierra visited Gaitán's office at 9:30 AM. Gaitán had arrived a little before 8 AM even though he had been awake until late because he attended the trial of Lieutenant Jesús María Córtez Poveda, a friend of his. One of Gaitán's security saw Roa Sierra with another person even though he solicited the interview alone. What happened in this interview is unknown but the man who was with Roa Sierra bore a face incredibly similar to Colonel Gustavo Rojas Pinilla.

Gaitán was assassinated minutes after 1:00 PM and later pronounced dead around 2:00 PM. Police corporal Carlos Alberto Jiménez Díaz and Sargeant Galvis González arrived at the scene as soon as the shots were heard. The news spread quickly and an enraged mob developed in short time yelling "mataron al doctor Gaitán" ("they killed Dr. Gaitán"). It was reported that Roa Sierra begged to Jiménez "no me mate, mi cabo" ("don't kill me, corporal"). Jiménez is also reported to have taken him hastily to a drugstore to protect him from the incensed crowd. The angry mob grew in front of the drugstore that was sheltering Roa Sierra. Finally the situation was so menacing that the iron shutters of the drugstore were opened. Roa Sierra's body was then kicked and stabbed by the massive mob until he was "an almost shapeless corpse"; then his body was left in front of the Presidential Palace.

Once the dust settled the police were finally allowed to collect what remained of Roa Sierra. What was peculiar is that the gun that Roa Sierra had on him was defective, it was missing a firing pin and no gunpowder residue could be smelt or seen. The revolver Roa had carried was incapable of accurate fire, Roa was not thought to have any firearms training, the assassination had been committed at some distance, and that no eyewitness saw Roa anywhere near the assassination, in fact he was first seen between two policemen.

Colombian General Secretary, Rafael Azula Barrera, and the President of Colombia, Mariano Ospina Pérez spoke on the assassination at 2:13pm in a snap conference that was broadcasted on radio and on the newly popular television:

PÉREZ: "Sons and Daughters of Colombia. Today is a day of mourning. We have lost a great Colombian statesman today. Although he was my opponent in this coming election, he was a great man who did everything in his power to insure Colombians would get the best outcomes possible. The horrendous act that took place today is not only a murder, but also an attack on Colombian democracy. Please, citizens of Colombia. Do not rise up in violence, this is a time for unity and friendship. In respect to the late Dr. Gaitán I will not be running for re-election, I'm sure Dr. Gaitán would support new candidates to guide Colombia during this incredibly sombre time."

BARRERA: "Thank you, President Pérez. As General Secretary of Colombia I have been privy to the police investigations that have already taken place. I would like to inform all of you that this murder is deeper than it seems. The assassin would not have been able to do such an act unless he had external support. Who in this world would get gain from the death of a beloved statesman? Who would get gain from the instability that it causes? Who would get gain from thousands and thousands of Colombians with misguided anger? I will tell you who, the Communist. The Bolshevik. The Soviet. Dr Gaitán was murdered as part of a conspiracy directed by an external Communist force to increase its red influence in the Caribbean. At this point we will not name names of those who we think are involved, but be assured that President Pérez is using the full extent of his power and knowledge to bring those involved to justice. Viva la Pérez, Viva la Colombia!"