(CNN) — [Breaking news update at 1:28 p.m. Wednesday ]
Boston University graduate student Lingzu Lu has been identified by the school as the third person who died in Monday’s bombings at the Boston Marathon.
[Original story, posted at 1:11 p.m. Wednesday]
(CNN) — 
The breakthrough came from analysis of video from a department store near the site of the second explosion. Video from a Boston television station also contributed to the progress, said the source, who declined to be more specific but called it a significant development.
Earlier, a federal law enforcement source with firsthand knowledge of the investigation told CNN that a lid to a pressure cooker thought to have been used in the bombings had been found on a roof of a building near the scene.
While such clues may move the investigation forward, they did not reveal whether the attack was an act of domestic or foreign terrorism.
Source: Tom Watkins, CNN
