A Munster, Indiana man has pleaded guilty to mailing a pipe bomb that exploded last year at a northwest Indiana post office.

Eric P. Krieg entered the guilty plea Tuesday to charges of knowingly making an unregistered destructive device, mailing a destructive device, malicious use of explosive materials and mailing a threatening communication, according to a statement from the U.S. Attorney’s Office for the Northern District of Indiana.

The Sept. 6 explosion last year injured a woman who worked at U.S. Post Office branch at 901 E. Chicago Ave. in East Chicago, Indiana, according to the FBI. The post office was not damaged and re-opened two days later.

Sketch of suspect who set off a pipe comb at the East Chicago post office. | FBI

Krieg, 45, was taken into custody a little more than a month after the explosion after he mailed another “suspicious package” that led authorities to search his home, workplace and vehicle, authorities said.

Between 2012 and 2017, Krieg used online forums and a blog he maintained to make a series of online postings and communications about other northwest Indiana residents, prosecutors said.

After a lawsuit based on statements Krieg made on his blog was filed in Lake County Superior Court in 2013, he filed for bankruptcy.

However, the attorney in the case, identified as “Victim 1,” claimed the suit couldn’t be discharged in bankruptcy, and Krieg agreed to pay the attorney’s client $45,000 and post an apology on his blog.

The package that exploded was addressed to the attorney, prosecutors said.

“In retaliation for the filing and settling of this lawsuit and other grudges I held, I devised a plan to construct and mail a pipe bomb that I hoped and believed would kill or injure Victim 1,” Krieg stated in the plea agreement. “I constructed this pipe bomb and knew that it contained explosives and items that would produce shrapnel.”

Krieg also admitted to mailing the second package containing a bullet and a message on Sept. 29, 2017 to a person he had interacted with online.

“I engaged in online communications with Victim 3.  Victim 3 was a resident of Northwest Indiana.  I was upset with, and held grudges against, both Victim 1 and Victim 3.  On September 29, 2017, I mailed a threat to kill or injure Victim 3.  I placed this threatening communication in the mail in the Northern District of Indiana and it was post marked to, and I am now aware later delivered to, Victim 3 in the Northern District of Indiana.”

Krieg agreed to a sentence of 29 years in prison as part of the deal, prosecutors said.