LOS ANGELES (AP) — Shares of several movie theater chain owners fell Friday after a gunman killed 12 and injured at least 50 others during the midnight premiere of Warner Bros.' "The Dark Knight Rises" in an Aurora, Colo., theater.

Cinemark Holdings Inc., the owner of the theater where the shooting happened, fell 97 cents, or 4 percent, at $23.30 in afternoon trading. The nation's largest theater chain operator, Regal Entertainment Group, fell 52 cents, or 3.7 percent, at $13.45. Smaller chain Carmike Cinemas Inc. was up 3 cents at $14.85.

Investors could be worried that theatergoers will be concerned about safety and limit their visits to theaters.

The finale of director Chris Nolan's Batman trilogy had been one of the most anticipated blockbusters of summer, with website Fandango reporting Thursday that advance ticket sales were outpacing this summer's comic book movie hit "The Avengers." The movie was on track to be one of its top-selling movies of all time.

Thursday midnight screenings brought in $30.6 million in the U.S. and Canada, the second-biggest midnight haul after the finale of the "Harry Potter" movies last year, according to Hollywood.com.

Some theaters and police around the U.S. stepped up security at daytime showings of the new Batman movie Friday after the massacre in Colorado.

Two police officers were stationed outside the AMC theater in New York's Times Square, which had showings of the Batman movie beginning every 20 minutes. Later in the day, the officers gave way to a police cruiser that was parked out front with an officer in it.

At a Regal Gallery Place multiplex in downtown Washington, theater employees searched patrons' bags and purses while taking their tickets.