If the "Army of God" has a website and known members, would they be so stupid as to sign the name of their organization to terrorist letters? If they did so and the FBI still can't find evidence to arrest them, the FBI is beyond hope. But if there is no evidence linking the "Army of God" to those letters, then PP is itself a suspect and should have left a trail. What is going on with the FBI?
If the "Army of God" has a website and known members, would they be so stupid as to sign the name of their organization to terrorist letters? Signing the name of an organization doesn't prove that the owners of a website who use that name are involved. As they claim on their site, the "Army of God" is a loose knit organization or merely a "state of mind".
If they did so and the FBI still can't find evidence to arrest them, the FBI is beyond hope.
I'm nop big fan of the FBI, but as long as people can send letters and packages anonymously, it's very difficult to pin down responsibility for terrorism by mail.