Audience members are lingering targets for an attacker, expert says Shooter had two handguns, a shotgun and AK-47-style weapon, federal official says Expert: Shotgun blast across row of theater seats could kill or wound 15 people Suspect in custody in deadly Colorado movie theater attack (CNN) -- A crowded theater offers an ideal location for a gunman -- particularly one armed with a shotgun -- to target dozens of victims, a weapons and security consultant said Friday. As investigators examine evidence at the Aurora, Colorado, movie theater where an armed attacker killed 12 people and wounded 38 others Friday, experts tell CNN the very nature of a large room such as a theater -- where people are seated in rows -- makes moviegoers easy targets, even for an inexperienced shooter. The gunman went to the rear door of the theater and propped it open, then tossed a tear gas canister before starting to shoot, according to a federal law enforcement source involved in the investigation. A suspect is in custody, and police said there is no evidence of a second gunman. Gunman kills 12 in theater shooting "If you're shooting in a movie theater, and you're near the exit or a main exit, you've basically got a turkey shoot," said Steven Howard, a Michigan attorney and security and firearms consultant. In this scenario, he said, audience members won't be able to escape -- making themselves lingering targets for an attacker. "The very nature of theaters makes them perfect killing zones," Howard said. A federal law enforcement official said the attacker had two handguns, an "AK-47 style" assault rifle and a 12-gauge shotgun. It's unclear which weapons were used in the attack. A shotgun would do more damage among a tightly packed theater audience because its ammunition comes out of the weapon in a reverse funnel shape and would disperse across a wider area, according to Howard. In a theater scenario, he said, "so many people's heads are lined up next to each other that if you fire down these rows of people ... one blast is going to kill or seriously injure 10 or 15 people, depending on a number of variables." An AK-47, Howard said, shoots one bullet at a time -- as opposed to a shotgun -- and that bullet "may go through two people." Most AK-47-type rifles use 30 or 35 round magazines, he said, and the weapons are not difficult to sneak into a theater under a long coat. No weapons expertise would be necessary to execute an attack such as the one in Aurora, Howard said. Any idiot can do it. The attacker also used tear gas, the law enforcement official told CNN. Tear gas and smoke bombs would "add to the panic" and make victims less likely to be able to defend themselves against an attacker, Howard said. The maximum deadly force of handguns is dependent upon how fast an attacker can change out ammunition, which is often contained in a clip or a magazine inserted into the weapon's handle. The dozens of wounded victims in the attack could well have been hit by ricocheting bullets. Once bullets hit a wall, they tend to ricochet down a wall, but they don't bounce like pool balls like a lot of people think and like the movies show. They follow the last surface they hit," Howard said. Crime scene investigators will likely pay close attention to the location of ammunition shell casings and bullets to learn more details about the attack. They also will likely document the locations where victims fell to determine the trajectory of the bullets. Share your tributes to the victims on CNN iReport.