A man who sent a pipe bomb in a package that caused an explosion last month at a post office in northwest Indiana was captured after he tried to send another suspicious package through the mail.

Eric P. Krieg, 45, was charged Thursday with knowing possession of a destructive device, and transporting explosive materials, according to the U.S. Attorney’s Office for the Northern District of Indiana.

Krieg, a Munster, Indiana, resident, mailed a package that exploded about 6 p.m. on Sept. 6 at the U.S. Post Office branch at 901 E. Chicago Ave. in East Chicago, according to the FBI and federal prosecutors.

After he mailed another “suspicious package” on Sept. 29, authorities searched Krieg’s home, workplace and vehicle on Oct. 12, and later arrested him, prosecutors said.

A postal employee was injured when the first pipe bomb exploded, the FBI said.

The woman was taken to St. Catherine Hospital in East Chicago, according to East Chicago police.

The post office, which sustained no damage in the blast, was reopened two days later, according to U.S. Postal Service spokeswoman Mary Johnson. There was no disruption in mail delivery service.

At least nine agencies helped with the investigation.