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Investigating the West, Texas explosion

07:46

President Obama spoke at the memorial service for 12 firefighters and first responders who died in a massive explosion at a fertilizer plant last week. Authorities still don't know what started the fire that detonated the highly-explosive material on site. MSNBC's Lawrence O'Donnell discusses with MSNBC's Alex Wagner and MSNBC.com executive editor Richard Wolffe.