Found something relevant on the Oral History of the Army, volume 10, pages 173-4. Not about the coup d'etat but of the Sergeants' Revolt in Brasília, September 1963, when Navy and Air Force personnel briefly occupied the city before being crushed by the Army, including paratroopers.

It is necessary to remember that there'd been an Army Police platoon's action in the previous day. That night, the Liutenant was Uchoa. But what happened to him? In the moment of the rebels' attack on the Air Ministry, he was with the platoon garrisoning and resisted the attack. Many shots were fired against his platoon. (...) He ordered fire because he had to stop the attack - it was really an attack. No soldier fired, no soldier fired. He took a soldier's rifle and behind a column spent the ammunition, rolled to another column - all soldiers were behind the Ministry's columns. He went soldier to soldier and resisted the attack himself, shooting, because the soldiers didn't.

The Army Library has a book, from 1958, "Men or Fire". I read this book a lot and if I'm not wrong it's General Omar Bradley's who did an inquiry on the Second World War on why man doesn't shoot, when in combat. After an operation in one of the Pacific isles, he put two or three regiments in "quarantine", so to speak, in a Pacific isle and heard from the commander to the last soldier. Where were you during the attack? What happened? Why didn't you shoot? Etc... And concluded, saying as follows: "The psychological factor". He has an interesting reference: the young man, mainly - it's our case that we incorporate recruits - he's raised to not mistreat even animals. It's that thing, don't tie a can to the cat's tail, don't mistreat the animal and from one hour to another, from seventeen to eighteen years he presents at quarters and we'll teach him to shoot to kill.

In face of this, when I was at the Agulhas Negras Military Academy: "We're here to teach you to kill, but to kill in the Fatherland's defense". Liutenant Uchoa was astonished. How is it that his soldier didn't shoot - there was no way to shoot! In the book, Omar Bradley says: "The best employment rate of troops in the Second World War was with paratroopers and commandos". Russian paratroopers had as much as 18% firing, at most 20%. In other words: of every infantry combat group only two men shoot when facing the enemy, even when he's running ten meters away. A combat group has a a sergeant and a corporal. If, of the ten members, two shoot, only the sergeant and the corporal fired. Not the soldiers. Recruits don't shoot, a lot of training is needed. A proof is what happened with Liutenant Uchoa.