From the Venezuelan constitution
Article 68: Citizens have the right to demonstrate, peacefully and without weapons, subject only to such requirements as may be established by law. The use of firearms and toxic substances to control peaceful demonstrations is prohibited. The activity of police and security corps in maintaining public order shall be regulated by law.
Judging from today's event the Chavez's administration has violated the consitution over and over. And from what we can see so far, the opposition had no firearms and we are waiting for the first casualty report from the repressive side.
Consitutions are only as good as the people that apply it.