The man who calls himself “The Bishop” and who has sent six threatening letters and two dud pipe bombs over the past 18 months is expected to strike again, the Associated Press reports. One of the pipe bombs was sent to American Century on Jan. 31. Then, on Feb. 1, a similar explosive was found in a Chicago office building.And next time, given that “The Bishop’s” letters have become increasingly menacing, the bombs could be real, warns Stratfor counterterrorism expert Fred Burton.

“He’s progressing,” Burton said. “He’s taking his thoughts, which in his mind are reality. He’s heading down a garden path of violence. It’s almost impossible to be able to tell when he will mail his next devices—but he will.”

Even though the post office, the Federal Bureau of Investigation, the Bureau of Alcohol, Tobacco, Firearms and Explosives and local law enforcement are involved and have released a sketch of a suspect in his mid-30s, catching the offender is going to be hard and will probably require the help of the public, Burton said.

Postal inspectors are offering a reward of up to $100,000 for information.

As to who the person is, Burton believes they are mentally ill, highly intelligent and a loner. But he might have a family, Burton added.

Subscribe Now

Access to premium content including in-depth coverage of mutual funds, hedge funds, 401(K)s, 529 plans, and more.

3-Week Free Trial

Insight and analysis into the management, marketing, operations and technology of the asset management industry.