President Barack Obama will head to Aurora, Colo., Sunday to meet with families of the victims of a shooting rampage inside a movie theater Friday that left 12 dead and dozens wounded.

In his weekly address Saturday, Obama said though authorities have learned that James Holmes is responsible, it may never be understood what lead the 24-year-old to commit multiple killings.

Such evil is senseless - beyond reason, Obama said. But while we will never know fully what causes someone to take the life of another, we do know what makes that life worth living. The people we lost in Aurora loved, and were loved. They were mothers and fathers; husbands and wives; sisters and brothers; sons and daughters; friends and neighbors.

And if there's anything to take away from this tragedy, it's a reminder that life is fragile, Obama added. Our time here is limited and it is precious. And what matters in the end are not the small and trivial things which often consume our lives. It's how we choose to treat one another, and love one another.

Police arrested Holmes without incident immediately after the shooting at Century 16 Movie Theater Friday. Patrons were watching the midnight premier of the new Batman movie, The Dark Knight Rises when the shooting rampage occurred.

Aurora Police Chief Dan Oates told the media that Holmes' shooting spree followed months of calculation and deliberation.

They recovered several weapons and managed to disarm his booby-trapped apartment in Aurora.

Authorities said Holmes was able to get his hands on multiple guns and ammunition through packages delivered to his home and school addresses. Four weapons found at the scene were bought at local gun shops, police said. The ammunition for those weapons was purchased on the Internet.

A total of 3,020 .223 rounds, 3,550 40 caliber rounds and 350 12-gauge rounds were found. Multiple .223 magazines were bought, including a 100-round drum magazine, police said.

Holmes was a graduate school dropout, but his friend Ritchie Duong, a student at UC Riverside, told the Los Angeles Times that Holmes didn't seem to change very much from high school.

We knew him as the same guy, Duong said. We would call him 'Jimmy James.' We would laugh all the time about it.

Everything came easy for him, he added. I had one college class with him, and he didn't even have to take notes or anything. He would just show up to class, sit there, and around test time he would always get an A.