-- While the clues moved the investigation forward, it is still unclear whether the attack was an act of domestic or foreign terrorism.
-- No connection has been made to any terrorist group or individual.
-- President Barack Obama described the bombings as an act of terrorism, but said it is unclear whether they were the work of a group or "a malevolent individual."
-- The Pakistani Taliban has said it was not involved in the attack.
-- Authorities don't have a sense of what the motive is, an official said.
-- The FBI asked the public to report anyone who talked about targeting the marathon or showed interest in explosives. The agency urged anyone who might have heard explosions in remote areas -- possibly by someone testing a bomb -- or seen someone carrying "an unusually heavy, dark-colored bag" around the time of the attack to come forward.
Three days later, authorities have yet to make an arrest, but have made "significant progress," a law enforcement official said.
-- Investigators have pinpointed two men of "high interest" as possible suspects after they appeared in images near the finish line moments before the blasts, a law enforcement official said.
-- One of the men is seen carrying a black backpack.
-- Authorities had not yet named the two, but their photographs have been distributed to law enforcement, a source said.
-- Earlier Wednesday, two sources with knowledge of the investigation identified a man as a possible suspect in the attack, but did not name him.
-- Seen on a video, the man wore 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.
-- It was not immediately clear if he is one of those alluded to in the photographs distributed to law enforcement officials.
-- Investigators are closer to cracking the case "every hour," Massachusetts Gov. Deval Patrick said. He urged patience with the probe to allow investigators space to do their job.
-- "I wish they had nailed the perpetrator within minutes of this catastrophe, but I understand from experience it's going to take some time," he said.
-- Significant progress has been made in the investigation, but there has been no arrest, the FBI told CNN.
-- After sources told CNN on Wednesday that an arrest had been made, sources with the Department of Justice and Boston Police Department each said that no arrest had been made.
-- A source with Boston law enforcement said, "We got him," but would not clarify whether that meant an identification had been made or an arrest carried out.
-- Some federal sources said that it would be going too far to say even that an identification had been made, but several sources in Boston disputed that, saying a clear identification had been made.
-- Investigators believe they have identified a suspect in the marathon bombings, a source who has been briefed on the investigation told CNN's John King. The possible breakthrough came from an analysis of video from a Lord and Taylor department store near the site of the second blast, and video from a Boston TV station helped as well, the official said.
-- As they scramble to search for suspects, authorities are processing "the most complex crime scene that we have dealt with in the history of our department," said Ed Davis, the Boston police commissioner.
-- Forensic specialists and dogs trained to detect explosive devices and their residue were at the scene of the blasts. A command post has been created, with 1,000 officers conducting interviews and gathering details.
-- Authorities have received 2,000 tips from around the world, said Richard DesLauriers, the special agent in charge of the FBI's Boston office. "Someone knows who did this," he said.