ATLANTA — The man who police say staged an assault on a Georgia courthouse carefully planned the weapons and supplies he would need to enter the building and harm people inside, authorities said Saturday as they sought to explain why Dennis Marx opened fire outside the building, wounding one deputy before dying in a shootout.

Police said they found a checklist at Marx’s home in Cumming, Georgia, that matched the items inside the rented silver Nissan SUV used in Friday’s attack. Marx had a number of bags and buckets holding homemade and commercial explosive devices that could be clipped to hostages; a gas mask; two handguns; zip ties and two bulletproof vests, police said. They said Marx, 48, wore one of the vests and clipped a hand grenade and wire to himself as a booby trap.

Investigators still have questions about any motive Marx, 48, had for the attack that began about 10 a.m. on the courthouse square in Cumming. Marx had been due in court to plead guilty in a drug case earlier Friday.

Deputy Daniel Rush, who first engaged Marx outside the courthouse, remained in stable condition Saturday after being shot in the leg.