LOS ANGELES: The release of Warner Bros.' movie “The Dark Knight Rises” brings to an end one of Hollywood's most enduring franchises, as the studio searches to find a new one capable of matching Batman's box office success.  

Forecasts for opening weekend ticket sales were thrown into doubt following a Colorado shooting on Friday at a midnight screening of the film in which 12 people were killed.

In New York, police planned to deploy officers at screenings of the film throughout the city “as a precaution against copycats,” Police Commissioner Raymond Kelly said in a statement. The Paris premiere of the film was canceled.

Warner Bros. said in a statement the studio was “deeply saddened” by the incident and extended sympathy to families of the victims.

The Time Warner-owned studio has been Hollywood's King of Franchises for years. Over the last decade it generated worldwide ticket sales of $12 billion from its “Lord of the Rings,” “Batman,” and “Harry Potter” films.

Eight of the 20 highest-grossing films of all time come from one of those franchises, according to website Box Office Mojo.

“The Dark Knight Rises” will be the last of the Batman series that began in 2005, director Christopher Nolan said.  “Harry Potter,” Warner Bros.'s biggest franchise, ended last summer with the largest of eight films, “Harry Potter and the Deathly Hallows - Part 2,” which generated $1.3 billion worldwide.

Franchise films are especially important to studios, amplifying their revenue by using the big-budget movies to create theme park rides, sell toys and spawn TV shows.

Warner Bros. is counting on a pair of “Hobbit” movies to rekindle the magic of “Lord of the Rings.” The first installment hits theaters in December.

A reboot of the “Superman” franchise is also scheduled for next summer - “Man of Steel,” made by “Dark Knight” producer, Legendary Pictures. Nolan, one of Hollywood's hottest directors, is a producer on that film.

The films could pave the way for Warner to unite Batman, Superman and other characters from its DC Comics stable in a “Justice League” movie, said Gitesh Pandya, editor of website Box Office Guru.

That would follow the strategy that brought staggering success to Walt Disney Co with “The Avengers,” a movie that brought together a handful of Marvel superheroes and generated nearly $1.5 billion in worldwide sales.

One problem for Warner Bros. is that not every DC Comics character has been a phenomenal hit, Pandya said. Last summer's “Green Lantern” didn't work very well, he said, grossing $219.8 million. Some industry watchers said the movie cost $200 million to produce, though Warner has disputed that figure.

Studios receive about half of box office sales. The 2006 “Superman Returns” also disappointed, Pandya said. The aim is to create another series like Batman, which won critical acclaim, fan devotion and $1.4 billion in ticket sales for “Batman Begins” in 2005 and 2008's “The Dark Knight.”

“The Dark Knight” grabbed $158 million in the United States and Canada on its opening weekend in 2008, a record at the time and still the highest debut for a movie that wasn't boosted by higher-priced 3D tickets.

Opening weekend ticket sales for “Dark Knight Rises,” which cost $250 million to produce, had been expected to at least match the last Batman film, according to box office forecasters, and possibly reach as high as $198 million, just shy of the $207 million record set by “Avengers” in May, some industry analysts say.

That was before the midnight showing Friday in Colorado erupted in violence, when a masked gunman in Aurora, a suburb of Denver, opened fire on an unsuspecting audience, killing 12 people and wounding dozens of others.

Beyond superheroes and the “Hobbit,” Warner also intends to bring “The Hangover 3” to theaters next summer, the next installment in the adult comedy series that has grossed $1 billion.  “We are well on the road to quite a number of franchises,” said Dan Fellman, president of theatrical distribution for Warner Bros. “We are in great shape.”