A written message that begins "To all the innocent souls... this is for you," is shown near a display of candles, flags, and other tributes on July 20, 2012, in Aurora, Colo. (Ted S. Warren/AP Photo)
AURORA, Colo. (AP) - Police in Colorado say the suspect in one of the worst shootings in U.S. history is not cooperating with authorities.
Aurora Police Chief Dan Oates says 24-year-old James Holmes has "lawyered up" and is not talking.
Holmes was arrested Friday after a gunman opened fire during a midnight screening of "The Dark Knight Rises," killing 12 people and injuring 58. He has been appointed a public defender and is scheduled to make an initial court appearance on Monday.
Oates says it could take months to determine a motive and police are working with FBI behavioral analysts.
The police chief says Holmes had more than 50 commercial packages delivered to his home and school address during the past four months.
Sunday afternoon, President Barack Obama arrived in Colorado to meet with families of those gunned down Friday.
Air Force One touched down late Sunday afternoon at Buckley Air Force Base in Aurora. The president's hastily arranged visit includes a private meeting with the victims' loved ones and meetings with state and local officials about the shooting at a busy multiplex.
It is Obama's second trip in less than a month to comfort Colorado residents. He made a quick visit in late June to Colorado Springs, where hundreds of homes were destroyed in the most devastating wildfire in the state's history.
The shock of Friday's mass shooting brought the presidential campaign to a standstill for the weekend.
Meanwhile, police have finished collecting evidence from the apartment where Holmes lived, but residents are still not allowed back into the building because of chemical hazards.
Aurora police said Sunday residents can retrieve personal items, but the building remains closed.
Investigators say they found a complicated array of booby-trapped explosives in Holmes' third-floor apartment. It took bomb experts hours to dismantle and dispose of the material.
Police don't yet know when the residents will be allowed to go home.
Holmes is suspected of opening fire on a packed movie theater early Friday, killing 12 people and injuring 58.
Police say the theater will remain closed as a crime scene for up to a week.