US President Barack Obama on Saturday promised justice to residents of Aurora, Colorado, who fell victim of a shooting spree at a movie theater that left at least 12 people dead.
"The federal government stands ready to do everything necessary to bring whoever's responsible for this heinous crime to justice," Obama said in his weekly radio and Internet address.
He also assured Americans that the government "will take every step possible" to ensure the safety of all the residents of the country.
Obama's comments came the day after a black-clad gunman in full body armor opened fire at a packed US movie theater in Aurora, creating a bloodbath which left at least 12 dead and nearly 60 injured.
Chaos erupted when the gunman tossed two tear gas or smoke grenades into the audience at a midnight showing of "The Dark Knight Rises," then gunned down terrified patrons as they scrambled for the exits.
Police arrested the suspect - identified as 24-year-old James Holmes - without encountering resistance by his car at the rear of the theater, in Aurora, a suburb of the city of Denver, in Colorado.
Obama called the assault an "evil" act which was "beyond reason." Visibly moved by the loss of lives, he urged Americans to think about the fragility of life and pay less attention to what he called "the small and trivial things," which often consume people's lives.
"It's how we choose to treat one another, and love one another," he said. "It's what we do on a daily basis to give our lives meaning and to give our lives purpose. That's what matters. That's why we're here."
The president promised to keep the victims of the shooting in his prayers and asked God to bring them "comfort and healing in the hard days to come."
US House Speaker John Boehner, who delivered the Republican address, called the shooting "senseless" and an act of "evil" it is difficult to comprehend.
"We join President Obama in sending condolences and prayers to the loved ones of those who were killed and wounded," the Republican leader said. "And we all say 'thank God' for the police, the first responders, the doctors, and the nurses whose swift and heroic efforts saved lives."