A U.S. District Court jury indicted Harpham on one count of attempting to use a weapon of mass destruction and one count of knowingly possessing an improvised explosive device.
Harpham was arrested earlier this month in connection with the bomb, which officials have said was "viable."
Last week, Harpham's father told reporters that his son is a racist and interacted with other racists online -- but maintained that he didn't plant the bomb. TPM has reviewed online postings at a forum for white supremacists that appear to have been written by Harpham.
Read TPM's full coverage of the case here.