This study is an analysis of the spread of information through Twitter contrasted with the reporting through a major Norwegian news network (TV2 Nyhetskanalen) during the terrorist bombing in Oslo and the massacre at Utøya July 22nd, 2011. The paper explores the impact of individual Tweets immediately before and after four key events: (1) the bombing of the governmental buildings in Akersgaten, (2) the first official reports of shootings at the Labour party youth camp at Utøya, (3) the arrest of the terrorist and (4) the publication of the identity of Anders Behring Breivik. Through tabulation of the potential audience for each re-Tweet received by the Tweets during these intervals, the goal is to determine the potential impact of Twitter as a social sensor and message bearer during dramatic events such as terrorist attacks. Through an extensive crawling of over 60.000 interactions, each Tweet's individual impact is shown to have reached audiences of several hundred thousand potential readers, often ahead of public reporting. This may be read in contradiction to earlier research, stating Twitter's prevailing tendency of being a reactive medium. The results also point to a changing relationship between eye-witness accounts and the public audience without media as an intermediate moderator.