President Luiz Inacio Lula da Silva vowed yesterday to uncover the “truth” of what caused a massive blackout across half of Brazil last week, and said everything would be done to avoid a repeat outage. His comments, made in his weekly radio address, underlined the mystery surrounding the blackout. With media questioning Brazil’s energy stability for the 2016 Olympics, Lula’s government initially blamed the incident on a storm, saying lightning must have shorted out transmission lines from the country’s biggest power plant. But that explanation was contradicted by official analysis of satellite data that showed there was no lightning strong enough at the time to have caused the outage.