John P. Tomkins, 42, of Dubuque, Iowa and an employee of a manufacturing company in that city, was arrested on his way to work and federal agents began searching his home, the U.S. attorney's office said.
A criminal complaint unsealed in Chicago charged Tomkins with one count of mailing a threatening communication with intent to extort and one count of possession of an unregistered explosive device.
A telephone message The Associated Press left at a number listed for a John Tomkins in Dubuque, Iowa, was not immediately returned. He was to appear at 2 p.m. Wednesday before U.S. Magistrate Judge Sidney I. Schenkier in Chicago.
Investigators have said "The Bishop" mailed more than a dozen letters to financial institutions for 18 months. The letters include references to heaven and hell and threatened recipients if the prices of certain stocks did not move to certain levels, often $6.66; the number '666' is associated with Satan.
"The way I see it, you owe it to us to make things right or I will make your life as miserable as mine is," one of the letters read.
Tomkins is a former substitute letter carrier who worked weekends for the U.S. Postal Service, authorities said. They said he no longer worked there when the devices were sent.
Officials said his letters were signed "The Bishop" and more than 100 postal inspectors investigated the case for months.
An affidavit filed with the court by postal inspectors said two parcels were mailed from Rolling Meadows in Chicago's northwest suburbs on Jan. 26. One was addressed to an individual at Janus Small Cap, a mutual fund, and at an address in Denver, officials said. That parcel was later forwarded to an office in Chicago. They said the other package was addressed to a person at American Century in Kansas City, Mo.
Each parcel contained what appeared to be a booby-trapped pipe bomb, officials said. They said that the firing circuit was not fully connected; otherwise the devices would have instantly exploded.
They would have thrown out a potentially fatal spray of fragments and shots if just one wire had been attached, officials said.
A letter in each parcel said: "BANG!! YOU'RE DEAD," authorities said. They quoted the letter as also saying that there would be a rally in the stock price of Navarre Corp., a technology and entertainment company.
The affidavit describes 16 other letters signed "The Bishop."
Among the other letters was one postmarked in northwest suburban Palatine on June 9, 2006, addressed to investment management executives that said: "TIMES UP ... IT IS BETTER TO REIGN IN HELL, THAN TO SERVE IN HEAVEN ... THE BISHOP."
One letter postmarked March 13, 2006, was addressed to a senior officer of Navarre Corp., complaining about the executive's pay and a decline in the stock price, officials said.
They quoted the letter as saying: "Within the next 60 days you are going to find a way to reverse the downward spiral of the stock price or the devil will be paying you a visit." It ended with the words "tic-toc" and was signed "The Bishop."
Officials said Tomkins' handwriting samples matched the writing on some of the envelopes that The Bishop mailed.
In addition, agents determined from a photograph contained in one of the mailings that the man they were looking for may have been driving a 1993, four-door Chevrolet Lumina -- the kind of car Tomkins owns.
Sales records from a home improvement store in Dubuque showed in December 2006 materials similar to those used in the pipe bombs were purchased with Tomkins' credit card.
Mailing a threatening communication with intent to extort carries a maximum sentence of 20 years in prison and possession of an unregistered destructive device carries a maximum of 10 years. Both carry a maximum fine of $250,000.