The FBI has begun to send pictures and other data from the crime-scene investigation of the Boston Marathon bombing to law-enforcement agencies around the country, including an image of a shredded black backpack in which one of the devices may have been hidden.  Reuters and the Associated Press managed to get copies of the unclassified bulletin and published a few of the images late in the evening, as did ABC:

The unclassified bulletin was sent Tuesday evening to law enforcement agencies across the country and said that the bomb inside the backpack was an “improvised explosive device (IED)” made out of a common pressure cooker. ABC News had previously reported that law enforcement recovered mangled parts of a pressure cooker bomb that included wires, shrapnel and a circuit board.

The advisory said there was “insufficient evidence” to determine if the second explosive, which was also hidden in a backpack less than a block away, was made from a pressure cooker as well.

Authorities have not yet determined the fusing system for the devices or what exactly set them off, the advisory said. The blasts erupted at approximately 2:50 p.m. EST near the marathon’s finish line Monday afternoon killing three people — including an 8-year-old boy — and injuring more than 170 others. Authorities have no suspects in the case and no group, domestic or international, has taken responsibility for the attack.

I find that pretty curious, actually.  Normally, terrorist groups use the media frenzy as a platform for their extremist agendas.  Obviously the media interest won’t fade away completely in the next couple of days, but the arc of media coverage will begin to wane significantly as normal news coverage returns.  Why wait to make the agenda for the attack known rather than take advantage of the short-lived terror it caused?

CBS has more of the images, and the FBI’s call for more:

Investigators believe the bombs were hidden in black nylon backpacks and housed inside the sealable metal pots called pressure cookers. Pressure cooker bombs can help boost the power of relatively small devices by briefly constraining the blast. And when the cookers do explode, they can add large chunks of metal to the shrapnel spray. …

The FBI and other law enforcement agencies repeatedly pleaded for members of the public to come forward with photos, videos or anything suspicious they might have seen or heard.

“The range of suspects and motives remains wide open,” Richard DesLauriers, FBI agent in charge in Boston, said at a news conference Tuesday. He vowed to “go to the ends of the Earth to identify the subject or subjects who are responsible for this despicable crime.”

Also, their “person of interest” is apparently not all that interesting after all:

Law enforcement sources told CBS News a Saudi Arabian man who was being questioned by investigators is not considered a suspect at this time, and it appears he was a spectator who was injured in the attack.

It was CBS that reported less than 24 hours ago that law enforcement was “really interested” in the Saudi national.  It’s just another reminder that these attacks produce a lot of data that turns out to be worthless in a short period of time.

The bulletin was the subject of a segment of Anderson Cooper’s show last night.  Why release the images in an unclassified bulletin?  For one, the FBI wants to jog the memories of the bomb-squad community:

Another reason might be to get a leak like this that encourages more people to send pictures and video of the marathon, both before and after the bombing.  It keeps the public engaged, and might shake loose some real leads.  Besides which, IED incidents are more common here than people think, although most of them are pranks:

In fact, in the last six months, there have been 172 IEDs reported in the United States, according to a government count that an official revealed Tuesday in answer to questions about U.S. preparedness. The official shared the figures, which were gathered before Monday’s explosion, only on the condition that neither the official nor the official’s office be identified.

The official shared information in an email that indicated most American IED attacks were small: “Homemade fireworks, childish pranks and other such non-terror related activities.”

But the information also notes that American officials have long understood the threat, and includes a warning that’s been distributed to other agencies: “Expect IED attacks by Homegrown Violent Extremists (HVEs) and individuals to continue throughout the United States. High profile events will present additional targets for HVEs and other individuals.”

Update: Via NewsJunkie, 4Chan tries a little dot-connecting:

Might be something, might be nothing — but this shows the wisdom of releasing the images, too.  Crowdsourcing, when properly managed, can exponentially multiply analytical power.  NewsJunkie has a lot more images of potential interest.