Prosecutors are considering pursuing a death penalty case against Holmes. A decision on charging Holmes with capital murder has not yet been made, but Chambers told reporters today she is talking with victims and their family members about it.
"If the death penalty is sought, that's a very long process that impacts [victims and family members] for years," she said.
Prosecutors have 60 days from the time of arraignment to decide whether they will seek the death penalty.
There are currently only three people on Colorado's death row, and two of them were put there by Chambers and her team. The last execution took place in 1997.
Nevertheless, experts expect prosecutors to seek the death penalty when Holmes is formally charged later this week.
The prosecutor said it will likely be at least a year before Holmes could go on trial.
"He has harmed so many people," Police Chief Daniel Oates said. "Not only the victims, but all of their extended families. So I think it will be very hard."
Oates' comments came before his department received a gag order Monday evening to stop police from discussing the investigation and instead defer to the district attorney's office.
"The Police Department's highest priority is the successful prosecution of this case," Oates said in a written statement announcing the gag order. "We are determined to achieve justice for the victims. We are well aware of the media and public interest in this case, but we ask for patience and understanding. Because of these orders, we simply cannot make any further comment. All of us must await the outcome of our judicial process."
Before the gag order, Oates told ABC News that Holmes' parents have remained silent.
"They're not talking to us right now," he said. "Maybe that will change, but right now they are not talking to us."
An attorney for Holmes' family today told reporters that the family is holding up "as well as anyone could under the circumstances," and that they still support Holmes.
"Yes they do. He's their son," said the attorney, Lisa Damiani.
The police chief told ABC News that his team is getting significant help from the FBI's behavioral analysts in trying to figure out what could have changed Holmes from a promising young student to a suspect in one of the largest mass shootings in U.S. history.
Authorities found a computer and Batman poster and a Batman mask from the comic books in his apartment, according to sources.
ABC News learned this weekend that Holmes apparently applied online for a membership at a local gun range last month. On the application, he apparently said he did not use drugs and was not a convicted felon. When Glenn Rotkovich, who owns the Lead Valley Range in Byers, Colo., called him to follow up, he said, he got a "bizarre," Batman-inspired voicemail message.
He told his staff not to allow Holmes into the club if he showed up for an orientation.
ABC News early Sunday obtained exclusive video and photos of Holmes as a thin teenager in an oversized shirt from a science camp six years ago at Miramar College in San Diego.
"Over the course of the summer, I've been working with a temporal illusion. It's an illusion that allows you to change the past," Holmes said in the video.
The video shows him being introduced at the seminar as someone whose "goals are to become a researcher and to make scientific discoveries. In personal life, he enjoys playing soccer and strategy games and his dream is to own a Slurpee machine."
ABC News' Dan Harris and Michael James contributed to this report.