Argentina: Protester killed in confrontation between labor unions · Global Voices
Jorge Gobbi

"Plaza de Mayo." Sign in the middle reads: "judgment and punishment for the murderers of Mariano Ferreyra." Image by flickr user Beatrice Murch, blmurch, used under an Attribution 2.0 Generic Creative Commons license
A confrontation between the members of the Ferroviaria Union (Railroad workers union) and workers that were protesting against layoffs along with militants of left-leaning parties, ended in the killing of Mariano Ferreyra, a student of the University of Buenos Aires and member of the Partido Obrero (Worker's Party). He was shot. By the time this post was written, his murderer had not been identified yet. Demonstrations condemning this event were quickly organized. The most important one took place this Thursday at Plaza de Mayo, a traditional space for protests in Buenos Aires, but there were also several mass meetings in other areas of the city.
Bloggers quickly reacted to the killing of Mariano Ferreyra. At the blog Todos Gronchos [es], the author says,
Al chico Mariano Ferreyra, hijo de una compañera mía del Magisterio Técnico de Avellaneda lo mató la corrupción, la complicidad entre los organismos de control; las policías bonaerense y Federal y los perros rabiosos de la Gendarmería kirchnerista, muy parecida a la de De la Rúa. Lo mató la ausencia del Estado, que se retira para que sus sindicalistas amigos se hagan más ricos y no le rompan las pelotas
At Mendieta El Renegáu [es] they focus on who came out to seek political benefits from the murder:
Todos salen a opinar tan rapido. Tan rápido. Insisto, opinan en la tele, en la radio, en tuiter y parecen contentos, todos parecen morbosamente contentos. A mí me dan asco. En especial aquellos que son dirigentes y que debieran dar el ejemplo al resto
Newspaper "Prensa Obrera" (Worker's Press) reads: "A crime against the working class." Image by flickr user archivo redeco, used under an Attribution-NonCommercial 2.0 Generic Creative Commons license
At El Buen Salvaje [es], blogger Mariano condemned the reaction of some government supporters:
Sí me sorprendió y me alarmó la reacción de mucha gente simpatizante del kirchnerismo que en twitter rozó el mal gusto, el revanchismo y la especulación sobre ‘la verdad oculta’ que se escondía detrás del asesinato de Mariano
A political evaluation in the same style can be found at Revolución Tinta Limón [es].  There were also references to attempts of manipulation from some official media in the blog Señales [es].
On Twitter there was no specific hashtag to organize the tweets, but you can search for “Mariano Ferreyra” to find tweets on the subject.