In the wake of one of the worst shootings in U.S. history, movie theaters across the nation are ramping up security to protect patrons and employees from copycat incidents.

Shortly after midnight Friday during a showing of “The Dark Knight Rises,” a gunman wearing a gas mask and black SWAT gear set off a gas canister and then opened fire inside a crowded theater in the Denver suburb of Aurora, Colo., killing 12 people and wounding 59 others, authorities said.

The suspect, 24-year-old James Holmes, was arrested near a car behind the theater. Authorities did not release a motive, nor is there any indication of ties to any terrorist group.

But some theaters are taking more precautions following the shooting. AMC Theaters, the nation’s second-largest chain, barred customers from wearing masks or costumes.

Some theaters were checking bags and purses while taking tickets, and others have added more law enforcement personnel.

Hollywood 15 Stadium Cinemas, Gainesville’s movie theater, deferred questions to its parent company, Georgia Theatre Company. Phone messages left Friday were not returned as of press time.

But local law enforcement said the business is one of the more “proactive” in the area when it comes to security.

“Like most businesses, we do have a good relationship with Georgia Theater Company,” said Officer Kevin Holbrook, spokesman for the Gainesville Police Department. “They’re actually a very proactive business when it comes to safety and security.”

Holbrook said the theater employs off-duty officers and has done so since its opening more than a decade ago.

The department also does security and threat assessments for the theater, as well as providing security education for its employees.

He could not speak to whether the theater was adding security measures following the shooting or not.

But he said officers, especially on weekends, patrol the business district thoroughly.

“Officers are aware of businesses as far as their patrols,” said Holbrook. “We try to stay on top of what’s going on in our nation ... and most officers know that typically weekends are busier for businesses, especially during a large opening like the Batman movie.”

And the department is trained for various scenarios, including chemical munitions, Holbrook said.

“Those are things that we, as a police department, do train on,” he said. “We are trained on chemical munitions and how to respond to chemical munitions such as mace, tear gas and things of that nature. Those are things we are prepared for.”

Holbrook doesn’t recall any incidents at Hollywood Cinemas in “a long while,” but said the business will have security — as always.

“At any given time, you’ll see an officer working there,” he said. “They are one of the more proactive businesses we do have.”

The Associated Press contributed to this report.