We have managed to narrow down the origin of the "federal law enforcement source" who told CNN's Fran Townsend on a Wednesday afternoon full of conflicting reports that there had been an arrest in the Boston Marathon case. The leak likely came from the FBI, although, really, the FBI wasn't too pleased about the "widespread reporting" with "unintended consequences." So maybe it was the Secret Service. Or the Bureau of Alcohol, Tobacco, and Firearms. Or Immigration, or Customs, or Homeland Security. Hell, maybe that "one law enforcement source in Boston" who told CNN's John King about the "game changer" arrest worked for the transportation authority cops. Really, on a day when confusion reigned, anonymous sourcing could have come from one of dozens of organizations and agencies and elected officials' offices involved in some part of the investigation. Here's the scope of what "law enforcement sources" look like in this case:

 

The Federal Bureau of Investigation (top right) is leading the effort. It has "hundreds of agents" involved in the investigation, both in Boston and the Boston area and at its headquarters in Quantico, Virginia. It is possible that one of those hundreds of agents in any of the locations was CNN's source — or one of its 36,000 other employees scattered around the world. The FBI is also a subset of the Department of Justice (top center), which itself employs thousands of people.

The agency also runs the Joint Terrorism Task Force (dark grey section at right), comprised of what it describes as "more than 30 federal, state, and local law enforcement agencies." According to its memorandum of understanding with the Massachusetts police, those include, at the federal level:

  • The Internal Revenue Service (second row, center)
  • The Bureau of Alcohol, Tobacco, Firearms, and Explosives (second row, right)
  • The United States Secret Service (third row, middle right)
  • The Department of Homeland Security (third row, right)
  • Customs and Border Protection (fourth row, right)
  • Immigration and Customs Enforcement (fifth row, right)
  • The U.S. Postal Inspection Service (sixth row, right)
  • The Naval Criminal Investigative Service (second row, left)
  • The Defense Criminal Investigative Service (third row, middle left)

 

The JTTF also includes, at the state level:

  • The Massachusetts State Police (state row, right)

 

And at the local level, it includes at a minimum:

  • The Boston Police Department (last row, right)
  • The Massachusetts Bay Transportation Authority Police (last row, left)

 

The rest of those 30 participating agencies are likely other municipal law enforcement agencies. Excluding those, the JTTF agencies have approximately 581,000 employees. But even that isn't the full extent of those involved in the investigation.

The role of the Department of Defense (top, left) isn't restricted to NCIS and the Defense Criminal Investigative Service (grey box, top left). It also manages the Massachusetts National Guard (third row, left), which is helping the City of Boston manage security. There are hundreds of Guardsmen on-scene.

It's also possible that one of the media's leaks today came from other organizations involved in the case. The office of governor Deval Patrick (state row, left), for example, has been intimately involved in the investigation. As has the office of Boston mayor Thomas Menino (last row, left). And representatives of Massachusetts' two senate offices and nine House offices. Each has likely been briefed and is providing to the investigation what assistance is possible.

As we noted earlier, CNN later revised its original, inaccurate report about the arrest. New York's news blog quotes:

Just a few hundred thousand suspects they'll need to sort through to find the source.