Authorities in Arizona say a man arrested in shootings targeting Democratic campaign offices near Phoenix had more than 120 guns and apparently had been plotting a mass casualty event.

(CNN) — 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,

TEMPE, Ariz. — A 60-year-old man suspected of shooting at a Democratic National Committee office over the last two months and hanging suspicious bags of white powder from political signs in a nearby village had over 120 guns and over 250,000 rounds of ammunition in his home and was preparing for a "mass casualty" act, according to prosecutors.