Yesterday, two bombs detonated at the finish line of the Boston Marathon, killing three and injuring more than 100 people. Here's everything we know about the bombing, its aftermath, and the hunt for the culprits.

Update, 3 p.m.

  • Investigators have found the circuit board thought to have triggered the explosive devices, the Globe's Shelley Murphy reports.
  • A second victim has been identified: 29-year-old Krystle Campbell of Medford, Mass, who was at the race with a friend to cheer on her boyfriend. Her friend sustained serious injuries and was in surgery overnight. The third victim is said to be an Asian woman. Below, photos of Campbell.

Krystle Campbell, 29, who died in the bombing. Photos via Facebook.

Update, 9:40 a.m. press conference

  • Despite reports of unexploded bombs (and controlled explosions) throughout the day yesterday, authorities have not found any devices beyond the two that were detonated. "Two, and only two explosives were found yesterday," Gov. Deval Patrick told reporters.
  • The injury count is now at 176, with 17 critical; Castle Park Plaza is open as a resource center.
  • The FBI is not commenting on the nature of the device; no one is in custody. The investigation is active, but there are no known additional threats. The FBI has received "voluminous" tips since the explosion yesterday. President Obama has pledged his full support; he is "actively involved and responding."
  • BPD is asking anyone who has photos or videos of the scene—before or during the event itself—to come forward. There will be an "enhanced presence" over the next few days: "more troopers, more national guard."

The scene immediately after the explosion, from photographer Aaron Tang's set of high-resolution photos taken from a nearby office building. [photograph by Aron Tang]

  • Authorities do not have a suspect and no one has claimed responsibility. Investigators have few leads, and the FBI has taken charge of the investigation, which will go something like this.
  • Federal agents searched an apartment in Revere, Mass. last night, looking for a person of interest, and "several bags" were removed from the scene early in the morning.
  • The "Saudi national" touted by the New York Post (among others) as a suspect all day yesterday is a student who is fully cooperating with police and denying all involvement. He has a clean record, and suffered burn injuries during the explosion. According to CBS News' John Miller, the man was tackled by a civilian because he was "acting suspiciously" and, uh, running away from the explosion.
  • The bombs were apparently packed with ball bearings and gunpowder in an attempt to maximize injury.

OWS Activist and projectionist The Illuminator lights up a message on the side of the Brooklyn Academy of Music. [via]

  • The latest casualty toll has three dead and 145 176 injured, including as many as 17 in critical condition. Several have lost limbs.
  • Martin Richard, an eight-year-old boy from Ashmont, Mass., is one of the three dead; his mother and sister were also seriously injured. The family was waiting in Copley Square for Richard's father to finish the race.
  • Two brothers from Wakefield each lost a leg from the explosion.

MIT's Green Building, across the river from Boston in Cambridge, was "hacked" to display a U.S. flag last night. [photo by @tochtli_exe]

  • Boston remains under high alert, and will entertain a heavy police presence today. Copley Square and the surrounding area will be closed to the public, as will Mass Pike Exit 22, Emerson and Berklee Colleges, and several nearby businesses. Bags will be searched on the MBTA.
  • Security has been heightened elsewhere as well: over a thousand cops were deployed in New York City yesterday, and the state was put on "heightened alert." In D.C., the security perimeter around the White House was widened and the police presence was increased.
  • Also beefing up security: Amtrak and Massachusetts nuclear plants, and LAX.
  • British police are reviewing their security plans for this week's London Marathon.

Today's Boston Herald, with a wraparound cover.