The tragedy in Boston continues to be a whodunit. The FBI held a press conference Tuesday afternoon to announce updates in their probe of the Boston bombings. Special Agent Richard DesLauriers said the investigation has recovered fragments of black nylon, BBs, and nails "possibly from a pressure cooker device" at the scene. "Somebody knows who did this," he said. The bureau announced it would bring in digital video experts from Quantico to dissect the "tremendous" amount of video police have turned over. On Thursday, President Obama will visit Boston to speak at an interfaith service.