Alexander Paffendorf, 20, of Carlsbad, was detained by FBI agents on suspicion of 'plotting' to coordinate a mass shooting at government buildings in conjunction with Rupnow, according to an emergency gun violence restraining order reviewed by the Milwaukee Journal Sentinel. It notes that FBI agents 'saw the messages from Paffendorf to Rupnow.' It was not immediately clear how Paffendorf knew Rupnow, and Madison Police Chief Shon Barnes told the Journal Sentinel he did not have any information about the arrest in California, and referred questions to the FBI.