(CBS News) Federal and local law enforcement searched an apartment in the Boston suburb of Revere, Mass., on Monday night, as part of the active investigation into the Boston marathon bombings.
Authorities say there is no clear suspect, but John Miller, a CBS News special correspondent and a former assistant director at the FBI, said Tuesday morning the latest focus continues to be "that apartment in Revere, on the person of interest that they've been interviewing since the bombing."
Miller explained that the Revere search warrant is part of the same probe as the questioning of a Saudi national who was hospitalized after the attack.
"All of that is the same," Miller said. "The Saudi national is ... here on a student visa. He was at the scene along with many other people when the blast happened. As everybody is standing in shock, three Boston PD detectives see this guy moving quickly out of the crowd. As they're watching him, he seems to be moving very deliberately away -- which could be a very natural thing after a bombing -- they stop him because he's covered with blood ... they think he may be injured...they engage him, they start asking questions ... there are things about his responses that made them uncomfortable, so they arranged to get him to the hospital."
"They stayed with him. The FBI has come along, they're talking to him. So he's somebody that they're really interested in."Special section: Boston Marathon bombings
The investigation is still in the early phases as authorities focus on combing through closed circuit camera footage, spectator videos and photos, and other evidence from the the scene of the blasts. "They're doing a grid on every approach to that location where the bombs went off," Miller said. "They're downloading every piece of tape from anything that recorded."
The two detonated devices will also provide critical information to investigators, who will "pick up every scrap, every fragment" to conduct chemical analysis. According to Miller, the early analysis indicates that the bombs were "not very sophisticated" and likely made with "something very simple like smokeless black powder, a low-order explosive ... but enough to do the job in a big crowd." He explained that it is too early to ascertain the bomber's so-called "signature," which could help authorities narrow down possible suspects.
"Where you find the bomber's signature [is in] how you twist the wire, what he uses as a fuse and they don't have all those pieces together yet."
While no group has claimed responsibility for the attack, Miller addressed speculation by lawmakers that it could be tied to al Qaeda or other foreign terror groups.
Miller acknowledged that it could be the work of al Qaeda, explaining that in the online al Qaeda magazine, Inspire, "they actually have instructions for these bombs, you see these simple bombs," but added that "we've seen these kinds of devices in domestic terror."