Two friends of the surviving Boston Marathon bombing suspect have pleaded not guilty to disposing of evidence from his college dormitory room. Dias Kadyrbayev and Azamat Tazhayakov were arraigned today in federal court on charges of conspiracy to obstruct justice. Prosecutors say the 19-year-olds from Kazakhstan tried to thwart the investigation of the deadly April explosions by throwing away fireworks and other items they found in the room of Dzhokhar Tsarnaev the day before his capture. Authorities found the fireworks in a landfill. If convicted, they face up to 20 years in prison.