LAS VEGAS (AP) — Las Vegas gunman Stephen Paddock's arsenal included tracer rounds that can improve a shooter's firing accuracy in the dark, a law enforcement official told The Associated Press on Friday.

It wasn't clear whether Paddock fired any of the illuminated bullets during the high-rise massacre Sunday night, but his purchase of 1,000 rounds provided more evidence of how methodically he planned the attack that killed 58 people and injured nearly 500.

Paddock bought the .308-caliber and .223-caliber tracer ammunition from a private buyer he met at a Phoenix gun show, a law enforcement of...