DENVER — The Colorado movie theater complex that was the scene of a shooting rampage this month did not have any uniformed security guards on duty the night of the attack, even though other theaters operated by the same company did provide such protection for the premiere of the new Batman film.

It’s impossible to know whether guards — often off-duty police officers — at the Aurora Century 16 would have spotted the suspected gunman, James Holmes, and thwarted the attack that left 12 moviegoers dead and dozens wounded on July 20.

Cinemark has arranged for off-duty police guards at the Aurora theater on busy Friday and Saturday nights. As for other nights of the week, theater operators decide on a case-by-case basis whether to hire security, depending on the likelihood of trouble. The attack came early Friday, shortly after the midnight screening of “The Dark Knight Rises’’ began.

The officers are generally armed and usually spend their time patrolling the complex, checking bags, or dealing with minor disputes.

Larry Lowak, whose son Brent was among the wounded, said security personnel possibly could have stopped the gunman, and he was dismayed to learn that guards weren’t on hand. Cinemark, based in Plano, Texas, declined to explain why guards weren’t provided in Aurora that night and declined to discuss security policies in general.

Through interviews with police officers and officials outside the theater chain, the Associated Press was able to identify other company theaters that did use armed security workers for the July 19-20 Batman showings — including those in Beaumont, Texas; Lake Charles, La.; and Tupelo, Miss.

Some other locations, including a Cinema Century 16 theater in the western Denver suburb of Lakewood, did not have security.

Aurora Police Chief Dan Oates has said the Cinemark in Aurora normally uses off-duty police officers to provide security on weekend nights but did not have any working for the July 19 showings that went into the next morning. The theater does not have an unusually high record of complaints or crimes, police Sergeant Cassidee Carlson said.

In Moosic, Pa., Cinemark has worked for years with off-duty local police officers— typically on Fridays and Saturdays — and authorities said they were asked to provide two officersthat night because the midnight showing of the Batman film was expected to be a major event.

Two major multiplexes in Amarillo, Texas, including one Cinemark facility, also ensured that off-duty uniformed police were present for the first screenings of the Batman film. Amarillo Police Corporal Jerry Neufeld said the town’s theaters made a point of asking for them on the busy opening night.

The Aurora shooting has stirred discussion about appropriate security precautions at gathering places commonly considered safe. Analysts say that security at public venues has increased substantially over the past decade, but they also note that it’s impossible to maintain complete safety at all times.

Officials have said the Aurora shooting suspect bought a ticket to the midnight showing and went into the theater as part of the crowd. A federal law enforcement official said Holmes is believed to have propped open an exit door in the theater as the movie was playing, donned protective ballistic gear, reentered, and opened fire.

Aurora police said the suspecthad an AR-15 assault rifle, a shotgun, and two .40-caliber Glock handguns.

Some theaters have added security guards for all nights of the week since the shooting, and police departments around the country have also conducted extra patrols at movie theaters, though it is not clear if those shifts will be permanent. AMC Theatres has barred people from wearing masks or bringing fake weapons inside.

Many theaters, including the Cinemark in Aurora, prohibit patrons from bringing in concealed weapons used for personal protection.

Lowak, the father of the shooting survivor,said he believes people carrying concealed weapons might have helped limit the bloodshed.

But Hubert Williams, former head of the Newark Police Department and president of the Police Foundation, said that the idea that average citizens with guns could keep a theater safe only makes sense ‘‘on a piece of paper.’’

‘‘Reality is much more complicated. What if you pull a gun out, take aim, and someone else thinks you’re the shooter?’’ he asked. ‘‘Would you stand up against an AR-15, AK-47 military-style assault weapon? Give me a break.’’