(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,

An Arizona prosecutor said the man arrested in the shooting of a Democratic National Committee office in suburban Phoenix had more than 120 guns and over 250,000 rounds of ammunition in his home, leading law enforcement to believe he may have been planning a mass casualty event.

Police linked the suspect with a suspicious white substance found on anti-Democratic signs after arresting likely suspect in multiple shooting attempts.