ABSTRACT The rise of online misinformation through social networks coincides with their growing use to stay informed and a polarised context that affects journalism and institutions. Beyond fake news, misinformation appears as a response to reality. Even the most dramatic events are subject to an online jury based on interpretative polarisation. This research analyses the case of the murder of Samuel Luiz, after a group aggression in A Coruña, Spain, during the secrecy of investigations. With a mixed-method approach we analyse media coverage (N1 = 159), public conversation on Twitter (N2 = 757,389), information disorders and the role of fact-checkers. The lack of information and the publication of some details fuelled a public conversation with ideological and political traits. The media coverage generated frames in which users position themselves for ideological and political reasons. The polarised conversation on Twitter was dominated by non-journalistic actors, with an important influence of the political position. The information disorders show that the noise generated by public discussion completes the story with false, misleading and biased content. Fact-checkers intervened, but their diffusion is limited compared to the volume of the debate on social networks.