UPDATE: The Boston courthouse has been cleared of spectators. Police scanner reports a bomb threat.
UPDATE: The Boston PD says there has been no arrest.
The Atlantic is updating with breaking news:
CNN and ABC Boston are reporting what had been imminent until now and remains in dispute: On air this afternoon, CNN's John King cited a local law enforcement official in saying that "an arrest has been made" after a "breakthrough" video provided "clear identification" of a suspect in the Boston Marathon bombing.
- Another CNN source said the same, telling reporter Fran Townsend that the arrest was made based on two separate videos. Law enforcement officials tell WBZ in Boston that "the person has been taken into custody by federal marshals and will be in court Wednesday afternoon." The Boston Globe also now says an arrest has been made, reporting that "official said authorities may publicize their finding as early as this afternoon." A news conference is scheduled for 5 p.m. Eastern. CNN is in the process of verifying its reporting and is stressing that this is breaking news. NBC News sources have been saying no arrest has yet been made.
- CNN's King had reported earlier that "substantial progress" has been made in the investigation: Boston officials believe they may have identified a bombing suspect. He said it was a "clear identification of a suspect" based on new video, obtained with help of a local TV station. King's law enforcement source in Boston called it a "significant breakthrough" and a "game changer," having been told there is "one suspect" — though this doesn't necessarily rule out a second suspect.
- A second source briefed on the investigation told King that department store video (apparently surveillance footage) from a local Lord & Taylor in Copley Square shows a clear facial recognition; investigators had been looking for video of a suspect placing down a bag and walking away. No confirmation of an arrest has been made and no identifying details have emerged other than what was described to King as a "dark skinned male individual." The Lord & Taylor would appear, from the above Reuters photo that appeared on the front page of today's New York Times, to have been the second blast site.