Here's what investigators have said they know, so far, about the Boston Marathon bombings that killed three and injured 183 people on Monday: The explosive devices used were built out of conventional pressure cookers placed in nylon backpacks. What they don't know: anything else. The "range of suspects and motives remains wide open [...] Someone knows who did this," Special Agent Richard DesLauriers, the lead investigator, told reporters. "[T]he person who did this is someone's friend, neighbor, coworker or relative." The Bureau is actively soliciting photographs, tips and information; examining the bombs; and using face-recognition software in an attempt to generate leads. No one has claimed responsibility, and the "Saudi national" briefly placed in custody after the bombing (whose suspecthood was loudly touted by the New York Post and Fox) is no longer a person of interest. It will be a "long, painstaking investigation," Massachusetts Governor Deval Patrick told WBUR this morning, but "every hour, every day" will get us "a little closer." [NBC, AP, image, of the Public Garden following an interfaith service at Arlington Street Church in Boston, via AFP/Getty]