(CNN) -- Investigators believe they have identified a suspect in the Boston Marathon bombings, a source who has been briefed on the investigation told CNN's John King exclusively.
The breakthrough came from analysis of a 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.
CNN Reports:
Investigators scrambling to solve the fatal bombings at the Boston Marathon want to question a man seen on video as a possible suspect in the attack, two official sources with knowledge of the investigation said Wednesday.
The sources identified the person as a man wearing a white baseball cap. One of the sources added that the cap was on backwards and the man was also wearing a light-colored hooded sweatshirt and a black jacket. The second source said investigators have not identified this person.
The news comes on a day when authorities have made "significant progress" in the case but no arrests, a federal law enforcement source told CNN's John King. Sources previously told CNN that a suspect was in custody, but both Boston police and the FBI denied that any arrests had been made.
In addition, a federal law enforcement source told CNN that "anyone who says 'arrest' is ahead of themselves."
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.
"If your experience and your expertise is Middle East terrorism, it has the hallmarks of al Qaeda or a Middle East group," former FBI Assistant Director Tom Fuentes said. "If your experience is domestic groups and bombings that have occurred here, it has the hallmarks of a domestic terrorist like Eric Rudolph in the 1996 Atlanta Summer Olympics bombings."Fuentes said he has investigated both types of terrorism -- from Iraq to the United States -- and finds the Boston attack has elements of both. "It has the hallmarks of both domestic and international (attacks), and you can see either side of that."