The violence comes from the "Colectivos", the police and the national guard. If the author of the article does not know what a "Colectivo" is then he/she should not be writing about Venezuela.
For those who do not know, "Colectivos" is a militia group that Chavez started years ago, they all have motorcycles, they travel in pairs and the government has equipped them with weapons. Where do these people come from? 98% of them are criminals, they kill for joy, they torture, represent and "defend" the regime. The police and military has been infiltrated by cubans, so they are under heavy control and if they don't do what they are told they are killed when they get back to the fort.
Yesterday one of them rolled his motorcycle, three times, over a fallen young woman, they beat up a 67 year old man, etc. etc. These people have lost all sensibility, they kidnap, kill with no remorse, it is the worst that human kind can produce.
That is where the violence comes from, not the opposition. If anything, the opposition's biggest mistake has been one of insisting to do things via the few democratic resources they have, and they shrink every day.