Witnesses say the suspect not only was heavily armed but he also used tear gas in the attack.
Many people thought it was part of the show when the gunman first deployed tear gas on the theater full of men, women and children, but they quickly realized it was no stunt when he opened fire with multiple weapons.
"To get all these people panicking and screaming, their eyes are burning, their all factories feel like they are on fire, they are going to be much easier targets," said Brian Hoffner, owner of Hoffner's Training Academy.
Hoffner, a SWAT team veteran, says tear gas is used legitimately by law enforcement. However, a quick search on the Internet shows tear gas is readily available online for anyone to purchase.
Investigators say after deploying the tear gas, he opened fire with multiple weapons.
"He used an AR-15 in the theater, a shotgun within the theater and a 40-caliber Glock," said Chief Daniel Oates with the Aurora, Colorado, Police Department. "In the end, he was in the possession of two 40- caliber Glocks."
Hoffner says America's latest mass shooting shows the need to be prepared -- not paranoid. He trains students to evaluate even the most innocuous situations.
"We don't sit in the middle, like where we can see the screen and enjoy the movie. You still enjoy the movie, but you do it from the aisle seat, because from the aisle seat close to the exit, you know where the exits are," Hoffner said.
Law enforcement officials in Colorado say Holmes purchased all the weapons legally over the last few months at several hunting and fishing stores.