This week's top news on YouTube: Journalists killed in Homs, soldiers killed in Afghanistan riots, Buenos Aires train crash

Everyday on the CitizenTube channel (and @CitizenTube on Twitter), along with our curation partners @storyful, we look at how the top news stories are covered on YouTube. Each week we post a weekly recap of the top news stories of the week, as seen through the lens of both citizen-reported footage and professional news coverage.

• We were shocked at the deaths of legendary war correspondent Marie Colvin and award-winning photographer Remi Ochlik, as well as citizen journalist Rami al-Sayed, who were killed while working to document what was happening inside Syria.
• We heard pleas for help from two injured journalists, Edith Bouvier of Le Figaro and Paul Conroy of the Sunday Times, who are still trapped in Homs. 
• We witnessed riots in Afghanistan that left two US soldiers dead, sparked by the burning of religious texts by NATO troops. 
• We followed the GOP candidates engage in what could be their last debate on the US campaign trail, while Mitt Romney continued to be dogged by controversy. 
• We saw carnage in Buenos Aires as a train slammed into the platform at Once Station, killing dozens and injuring hundreds. 
• We watched the frozen River Danube, which caused trade along the river to be disrupted, begin to thaw, causing problems of its own. 
• We observed mixed emotions as Yemenis turned out to vote in their presidential elections, even though there was only one name on the ballot card; vice president Abdurabu Mansur Hadi. 
• We viewed the skiing world mourn the loss of three of its members, who were killed in a Washington State avalanche. 
• And finally, we celebrated Carnival in style with Brazil, as cities like Rio de Janeiro were packed with music and revellers.