No word on what’s happening yet but the photos don’t look good:

https://twitter.com/RosieGray/status/323873105816719360
https://twitter.com/NightShiftPol/status/323872730409734144

Note that there’s blood on the ground in the second pic. Standby for updates.

Update: Oh boy.

MCI: 20-30 people injured in front of Boston Public Library after explosion at finish line of Boston Marathon

— Boston_Fireman (@Boston_Fireman) April 15, 2013

Unconfirmed reports of two explosions.

Update: Hard to tell for sure from the top pic but it looks to me like the explosion might be coming from inside the building.

Update: John Ekdahl is watching Fox News and says the mic picked up someone at the scene saying, “Oh my God, they’re dead.” And there do appear to have been two explosions, the second one of which was bigger than the first per George Scoville. That’s a terror tactic: Set off a smaller explosion to get a crowd moving into an area where a bigger bomb is waiting for them. But I don’t mean to jump to conclusions. More updates coming.

Update: It’s as bad as you fear.

https://twitter.com/JackieBrunoNECN/status/323876567950426113

Update: Someone on Twitter points out that it’s Patriots’ Day in Boston, when Lexington and Concord are commemorated, in case you needed another reason to suspect this is terrorism.

Update: Worse and worse and worse.

Bomb at #Boston #marathon finish. pic.twitter.com/6ppZ0Rxs3M

— Bruce Mendelsohn (The Hired Pen) (@brm90) April 15, 2013

Update: Another device found? Often these early reports are wrong:

https://twitter.com/911BUFF/status/323879446299942912

Update: An eyewitness says there must be “dozens” of people seriously injured.

Update: Ed Henry tweets that Fox is reporting at least three dead.

Update: The Boston Globe says the Lenox Hotel is now being evacuated. Whether that’s because something’s happening there or if it’s simply cops being cautious is unclear. There are also reports of a device at the JFK library, but again, that may simply mean “suspicious (yet ultimately harmless) package.”

Update: In response to the update above about Patriots’ Day, Ace’s co-blogger DrewM reminds me that it’s Tax Day too, of course. Maybe significant, maybe not.

Update: Vine video of TV footage showing the moment of the explosion.

Update: This is exactly how it felt in midtown Manhattan about an hour after the towers collapsed:

rt @billy_baker Calm, nervous energy in Copley. Many don' know. Others can't figure out where to go. Too many people. Feels dangerous.

— The Boston Globe (@BostonGlobe) April 15, 2013

One very obvious element to an attack that I never appreciated until 9/11 was that you simply don’t know when it’s over. I thought more planes were on the way, or maybe something worse.

Update: Reports of other bombs are getting more credible:

Boston police say 'secondary devices' still being found: @BostonGlobe | http://t.co/YWW7fcmSki

— Bloomberg (@business) April 15, 2013

Update:

Update: From the Boston Phoenix:

Police officer near Boston Marathon finish line: 'There are secondary devices that have been found and are unexploded.'

— Chris Faraone (@Fara1) April 15, 2013

Update: Fox News evidently has reason to believe from its sources that ball bearings were used in the attack.

Update: CNN says there are two dead, Fox claimed earlier that were three, but we now have two networks claiming multiple fatalities.

Update: Not an accident, needless to say:

BREAKING: Small homemade bomb is preliminary cause of explosion at Boston Marathon, law enforcement officials tell NBC News

— NBC Nightly News with Lester Holt (@NBCNightlyNews) April 15, 2013

Update: Nick Kristof senses a political opportunity and lunges.

Update: Sounding now like those other “suspicious packages” were more than just suspicious:

BREAKING: Multiple explosive devices found, at least 2 which exploded, officials tell NBC News

— NBC Nightly News with Lester Holt (@NBCNightlyNews) April 15, 2013

One of the amazing things about this attack is that security would have been tight naturally for the marathon. The plotter or plotters somehow snuck three or more bombs in under the noses of Boston police:

Big city authorities are typically on the highest levels of alert for events like a marathon, said Anthony Roman, a security expert.

“It is quite the counterterrorism effort,” said Mr. Roman, who runs Roman & Associates, a New York firm.

For major events in New York and other large cities, Mr. Roman said the police would typically weld manhole covers shut, while also examining the entire route just before the race. They will also place snipers on rooftops, with helicopters overhead. Analytic cameras in the city will be focusing on the race, he said.

“They have all the analytic cameras in the city focusing on the race with their advanced software network, reading license plates,” Roman said.

How’d the plotters do it?

Update: Hmmm. According to a Boston Herald reporter, the blast “ looked like it was in a trash can or something.”

Update: Four bombs now:

WASHINGTON (AP) _ Intelligence official: 2 more explosive devices found at Boston Marathon; being dismantled.

— Ken Thomas (@KThomasDC) April 15, 2013

Update: We’re now two hours into this and I’ve yet to see any reports that these were suicide bombers or car bombs. Maybe too early to tell, but if this is AQ, the usual M.O. appears not to have been followed.

Update: The New York Post is the only outfit I’ve seen reporting this, but their sources should be solid:

A federal law-enforcement source confirmed to The Post there are at least 12 dead and nearly 50 injured. Fox News reported that Massachusetts General Hospital was treating 10 people with amputated limbs and all operating rooms were on hold.

Authorities have a identified a suspect, who is currently being guarded in a Boston hospital with shrapnel wounds.

Other sources said that the first explosion did in fact go off inside the lobby of the Fairmont Hotel, just as it looked from the first photo above.

Update: Did the cops get a tip?

https://twitter.com/SalenaZitoTrib/status/323894620763340800

Update: I couldn’t load the Boston Globe earlier but it’s up now and they’re liveblogging on their home page.

Update: The Atlantic has a photo gallery. Number eight is gruesome, so take care before you click.

Update: Another report of bombs hidden in trash cans.

Update: The Post’s sources now claim the suspect is a Saudi national. Ace is wondering on Twitter, though, why a suspect would have shrapnel wounds. Good question. If he’s a suicide bomber, the bomb would have killed him. If he’s not, why hang around the area when the bomb goes off? Wouldn’t surprise me if the “suspect” ends up being innocent.

Update: Via the Boston Globe, here’s video of the explosion. Sheer terror. Click the image to watch.

Update: Boston PD is giving a presser now, and the commissioner’s making it sound like the explosion at the library was also a bomb. That’s three in total; he says they haven’t found other devices. Meanwhile, another detail from that Post report on the suspect:

In addition, Boston police have has surveillance video of someone bringing multiple backpacks to blast site, according to CBS News.

Update: Three bombs or four? ABC’s Boston affiliate reports, “A senior U.S. intelligence official said two more explosive devices were found near the area, and they were being dismantled.”

Update: Fox News is now reporting that a “person of interest” is being held by police.

Update: Hmmmm:

According to CBS News correspondent Bob Orr, two bombs were inside trash cans near the viewing area close to the finish line. One unexploded device has been recovered, according to CBS.

Orr is reporting that authorities have recovered surveillance video from the area which shows a man with what looked to be two backpacks near the scene just moments before the blast.

Update: Have there been any casualties reported from the JFK library explosion? If not, and that’s how it sounds, that strikes me as unlike AQ too. Typically they aim for a body count above and beyond purely symbolic attacks, as an attack on a presidential library would be.

Update: Now I’m really confused. Was there no bomb at all at the library? Why did the police chief suggest that there was?

Fire in building is out, appears to have started in the mechanical room of new building. All staff and visitors are accounted for and safe.

— JFK Library (@JFKLibrary) April 15, 2013

Yep, Boston PD now saying that the library incident was “fire-related.”

Update: Interesting that the Boston Globe picked this tweet up for its liveblog. No proof that the arrest is related to the attacks, but the National Guard showed up on the common shortly after. Then again, why wouldn’t they? They’re locking down public spaces after a bombing:

https://twitter.com/Eric_Twardzik/status/323911455252553729

The author of the tweet updated to say that he believes the suspect’s wearing just a white baseball cap, not a hoodie.

Update: Boston’s police chief, who was wrong earlier about the JFK library, now says there’s no suspect in custody. Whether that means the Post is wrong or that the cops don’t feel comfortable yet classifying their “person of interest” as a “suspect” remains to be seen. Could also be that my suspicion up top is correct: That he had nothing to do with the attack and they’re working on clearing him.

Update: In case there’s any remaining mystery about what happened, CNN reports that the FBI’s now calling it a terrorist attack.

Update: Chris Matthews stays focused on the big picture. The fact that he and Al Sharpton are the best MSNBC can do to anchor a terrorist bombing during prime news hours is amazing.

Update: So it’s four bombs after all.

https://twitter.com/jakeacarpenter/status/323924734385483777

Update: Obama spoke a few minutes ago but held off for the moment on calling the attacks “terrorism.” It could, I guess, be some sort of disgruntled nut who’s mad at the city or his boss or whatever and lacks any clear political motive, a la James Holmes or Jared Loughner. That’s now how I’d bet, but O would eat a mountain of shinola if he called it terror and then it turned out to be something else. He’s playing it safe for today. Lesser WH officials are willing to be bolder:

A WH official says while this is "clearly an act of terror" and will be treated as such, there needs to be invest to determine specifics

— Chuck Todd (@chucktodd) April 15, 2013

Update: One of the two people confirmed dead … is an eight-year-old.

Update: CBS is now backing up the Post’s claim about a Saudi national:

JUST IN: @JohnMillerCBS reports that individual is in custody after Boston blast, a Saudi national. Reported cooperative/denies involvement.

— CBS News (@CBSNews) April 15, 2013

Doesn’t mean he’s their guy. Could simply be that they noticed he was from the Kingdom, thought of 9/11, and decided to look more closely. More from the Times:

Police officials said they did not yet have any suspects in custody. A person briefed on preliminary developments in the investigation said that members of Boston’s Joint Terrorist Task Force were at Brigham and Women’s Hospital interviewing a wounded man seen running from the scene of the two blasts, near 671 Boylston Street. The person said that police investigators had contacted the local gas and electric company and determined that the explosions were not related to gas or electrical service.

The authorities also found a device at St. James and Trinity Streets that did not explode, the person said, and two other devices were found, including one in Newton, outside of Boston.

So there were … five bombs? ABC is also claiming that they were triggered remotely, which you could have guessed from the apparent fact that they were placed in garbage cans. As noted earlier, that’s not AQ’s usual M.O., but they have famously tried to remotely detonate car bombs in a terror plot in a major western city once before.

Update: I’m about to hand things off to Erika for evening coverage, so let me leave you with a question: What’s in Newton? Why would a terrorist bother with them? The only thing I can think of is that maybe that’s where he was living and planted something nearby out of convenience before making his way into Boston today.