The Washington Post reports on the difficulties Western intelligence agencies face in infiltrating al Qaeda and other terrorist organizations. The piece notes that fresh recruits are often "highly disposable," employed mainly as suicide bombers and general cannon fodder, making it difficult for informants to penetrate the networks. It also notes that those informants who do work their way up risk being exposed by the civilian justice system:

In January, Spanish police arrested 14 men in Barcelona who they suspected were preparing to bomb subways in cities across Europe. Investigators disclosed in court documents that the arrests had been prompted by a Pakistani informant working for French intelligence.

The revelation infuriated French officials, who were forced to withdraw the informant -- a rare example of an agent who had successfully infiltrated training camps in Pakistan. Spanish authorities expressed regret but said they had no choice; after they failed to find bombs or much other evidence during the arrests, the case rested largely on the informant's word.

This is why terrorists can't necessarily be allowed to see all the evidence against them. But it is problematic. What if 14 foreign nationals were arrested on American soil under similar circumstances? Would the federal government jeopardize a highly placed informant inside al Qaeda--one who had demonstrated his worth by averting at least one attack--for the sake of meeting the same standards applied in prosecuting mobsters?