"Bang! You're dead," read one of the notes seen by private counterterrorism analyst Fred Burton of Stratfor.com.
"I don't think this is a crank," says Burton. "It would not be something the average person would do. His communications are threatening. They are scary."
Burton, who provides security intelligence to business clients, says "The Bishop" first surfaced two years ago with a series of threats were mailed from numerous states in the Midwest, containing demands that companies manipulate stock prices. (Click here to read Stratfor's report on "The Bishop.")
He's made references to D.C. sniper Lee Boyd Malvo and convicted Unabomber Ted Kaczynski, who terrorized the nation with a 17-year mail-bomb campaign.
"...It is so easy to kill somebody it is almost scary," wrote "The Bishop" in 2005. "TIMES UP," he warned a year later.
Now, by including actual explosive devices with his threats, the suspect is upping the ante, says CBS News homeland security consultant Paul Kurtz.
"Definitely worrisome. You have an individual who's frustrated, who has sought some level of attention and hasn't received it. He's been blown off," Kurtz says. "Now, he's escalating."
The FBI confirms that at least one of the devices was a "functional pipe bomb," but neither exploded. Federal agents have traced the postmarks on mailings to a suburban Chicago post office.
But "The Bishop" remains at large.
"He's probably gone to ground, he's hunkered down and he's waiting for the next move on law enforcement," Burton says.
Burton believes the suspect, much like the Unabomber, is likely a loner with a grudge. But it may take a lucky break — a fingerprint or perhaps some DNA evidence — before police can make a move on "The Bishop."
MMVII, CBS Interactive Inc. All Rights Reserved