Jeffrey Michael Kelly, 60, was also arrested on suspicion of leaving white powder on political signs in Ahwatukee, according to Tempe police.

Arizona investigators surveilling the man accused of shooting at the Democratic National Committee office in a suburb of Phoenix saw him posting political signs with bags of a white, powdery substance attached,

The man, Jeffrey Michael Kelly, 60, was arrested Tuesday, according to the authorities. Mr. Kelly also set out anti-Democratic Party signs lined with razor blades near his home, attaching bags filled with an unknown white powder and labeled “Biohazard,” according to court papers.