Corruption spreads in South America

From Perú, to Brazil and Argentina leaders are mostly corrupt; the question is wheter a candidate is more or less corrupt than others. Sometimes politicians are punished and involved in trials and sentences, like the recent cases in Perú and the current case in Brazil with Dilma and Lula. But at the same time, a huge cloud of doubts appears when clearly corrupt ex-presidents aren´t judged for their offenses, which is what is happening in Argentina with ex-president Cristina Kirchner, who is currently running for Congress. In Brazil, the same thing happens with Lula, who is also running for office.All these events, make the people lose faith in the current government and the state. Where are the check and balances if major crimes go unpunished?