Where are you tonight, Sweet Marie

There is an almost theoretically unsolvable problem associated with the interface between law enforcement and crime.  On the one hand, law enforcement must have intelligence--it is not reasonable to expect law enforcement to remain entirely unsullied by association with criminals, since their job is to stop criminal activities.  On the other hand, to obtain intelligence is to frequently establish on-going relationships with criminals, to know in advance that criminal acts are being planned or even are occurring, to allow certain informants to continue their criminal activities in the service of catching other criminals, and so forth.  And so, with this nether world, comes the art of Noir (including LeCarre), and various real-life mysteries which must be taken into account by anyone trying to understand the real world.

E.g.  Jack Ruby was a long-time police informant at both the federal and state levels, and Lee Harvey Oswald himself appears to have worked for the US government at certain times in his life.  E.g., the events known as the Greensboro Massacre, in November of 1979, include the fact that a police informant rode in the lead Klan car, and led the shooters to the rally, where, oddly, no police were present.

Then there's this current event, the thwarting of an alleged bomber in Portland, Oregon, last weekend.  Glenn Greenwald writes a good piece on the involvement of the FBI, beforehand:

http://www.salon.com/news/opinion/glenn_greenwald/2010/11/28/fbi/index.html

For details of the Greensboro Massacre, see:

http://en.wikipedia.org/wiki/Greensboro_massacre

I'll quote one paragraph from the Greensboro story: 

"The marchers killed were: Sandi Smith, a nurse and civil rights activist; Dr. James Waller, president of a local textile workers union who ceased medical practice to organize workers; Bill Sampson, a graduate of the Harvard School of Divinity; Cesar Cauce, a Cuban immigrant who graduated magna cum laude from Duke University; and Dr. Michael Nathan, chief of pediatrics at Lincoln Community Health Center in Durham, North Carolina, a clinic that helped children from low-income families."

My daughter was grade school friends with the daughter of Dr. Nathan.  Both she and Dr. Nathan's daughter were born in 1979.   For a deeper understanding of the abstract problem of intelligence, see Peter Dale Scott's "Deep Politics."