From a BBC news summary:

In the 60 days leading up to the cinema attack, Mr Holmes legally bought four weapons at local gun shops - an AR-15 semi-automatic rifle, two .40-calibre Glock handguns and a 12-gauge Remington shotgun.

Chief Dan Oates of Aurora police said he also purchased more than 6,000 rounds of ammunition on the internet, including 3,000 rounds for the assault rifle, 3,000 for the Glocks and 300 for the shotgun.