I was thinking about that and reminding myself that next time I taught a class on taking someone down and controlling them in a street context that I should emphasize the importance of checking them for weapons. Maybe randomly give some students practice weapons to hide on their person that they can pull out if their partner doesn't check them properly.
That is an excellent idea. There's a clip I recall seeing in which a man who clearly has some grappling skills is confronted in a parking garage. Our guy takes the person down and (if memory serves) has them in an arm lock. At which point the bad guy pulls a knife from under his shirt and begins stabbing the grappler.
But in this particular case, it's not 100% clear from the information available whether it would have made a difference if Lo had patted down the murderer before letting him up. We don't know if he had the gun on him at that point or if he went out and got the weapon from his car after being subdued. Also, apparently the suspect was an off-duty police officer. I don't even know what the protocol would be in the U.S. if I took down and disarmed a crazy-acting drunk and he turned out to be a cop and the gun was his service pistol. I definitely don't know what the best practice would be in Brazil, which apparently has a serious problem with police corruption.
My knowledge of the legal situation is Brazil matches yours quite precisely. However, I know the law on this matter here in Colorado. Partly because it's a really good idea to know the applicable laws if you're going to carry (it's one of the things you're tested on when you apply for a CCW permit) and partly because everyone in my family seems to be either a teacher, medical, or LEO. One of our sons and a son-in-law are local PD. Another in-law is FBI. The law here is unusual in there is no obfuscation. It's plain, simple, and to the point.
C.R.S 18-12-106, it is illegal to carry a firearm while under the influence of alcohol or a controlled substance.
Note that it says "under the influence", not "intoxicated". A person is intoxicated if they have a BAC of 0.080 or higher. You are under the influence if there is any alcohol (or any other intoxicant) in your system.
Which works out great for my friends an family, because there's never any question of who will be the designated driver. It also means there is always at least one person in the group who isn't burdened by an abundance of beer-muscles.
So here, at least, the off-duty cop is 100% wrong. My cop-kids assure me that you would not be facing any legal issues if you took them down and disarmed them.
The story posted indicates that the BJJ fellow took down the other guy and had him restrained. In that situation, letting them up is a mistake, I think. You've got them controlled. Sit on them until someone (police, bouncers, club security, whoever) has them in hand.