JEFFREY BROWN: Once again today, Americans absorbed the news of a mass shooting, a dozen dead, at least 59 hurt or wounded. It happened in the city of Aurora, just east of Denver, where a movie theater erupted in late-night chaos.
NewsHour correspondent Tom Bearden begins our coverage.
TOM BEARDEN: The attack at the Century 16 theater set off terror and confusion. One man bore a long bloodstain across his back.
MAN: Did somebody get shot?
WOMAN: He got shot. Look, there's blood over there.
TOM BEARDEN: The deadly events began minutes earlier, during the showing of "The Dark Knight Rises," the new Batman movie.
MAN: I heard the sound of metal canisters clinking around, and then I saw plumes of smoke.
TOM BEARDEN: A man in a gas mask standing in front of the screen threw a tear gas canister, then opened fire.
DONAVAN TATE, eyewitness: I didn't realize there was something wrong right away. I thought -- I thought it was like a firecracker or a firework or something. I thought someone was just like, oh, it's the Batman premiere, I'm going to bring some firecrackers in and throw it and get people riled up.
TOM BEARDEN: But an instant later, it was clear the gunman was standing there, firing at people just a few feet away.
SILVANA GUILLEN, eyewitness: And like, all you could see is pretty much like the mask, just the gas mask. And it was probably one of the scariest images I have ever seen in my life.
And he just threw up the gun and just started doing it, and shooting, like, at least like four or five rounds, and then that gun ended, and then he just did it again with the other gun.
DONAVAN TATE: It was just chaos. All you -- you saw injured people. You -- there was this one guy who was on all fours crawling. There was this girl spitting up blood. There were bullet holes in some people's backs, some people's arms.
CHANDLER BRANNON, eyewitness: And we were just scared and didn't know what to do. And the guy unleashed about, like, maybe 60 to 70 shots. And after that was over or whatever, me and my girlfriend were playing dead in the aisle before that was over. And then after that was over, I heard somebody say, he's gone.
TOM BEARDEN: One of the victims was Jessica Ghawi, who escaped a shooting at a mall in Toronto just last month.
Benjamin Hochman was a colleague at The Denver Post. He says she will be sorely missed.
BENJAMIN HOCHMAN, The Denver Post: She was new to town, and she hung out with a lot of my friends. And she was a budding journalist and just a budding personality. I spent a lot of time with her, and every time I did, we just laughed and laughed.
TOM BEARDEN: Happy person?
BENJAMIN HOCHMAN: She was effervescence. Effervescence is the best word to describe her, just bubbly, so much fun to be around, quick with a joke, a goofy person, and she just lit up the room.
TOM BEARDEN: As they surged outside, shocked moviegoers tried to understand what had happened. And police arrived and made an arrest in a matter of minutes.
DAN OATES, policy chief, Aurora, Colo.: This event began at 00:39. So, 39 minutes after midnight, the first calls into 911.
I'm told by a colleague you could describe it as hundreds of calls coming in. Within roughly one minute to a minute-and-a-half, police officers were on scene. He was apprehended with three weapons in the car, and one was left at the scene inside the theater.
The weapons are as follow: an AR-15 assault rifle, a Remington 870 shotgun, 12-gauge shotgun, and a .40-caliber Glock handgun. We believe those three weapons were used in the scene, and another .40-caliber Glock handgun was found in the car. We're not sure if that was also used in the scene.
The suspect was dressed all in black. He was wearing a ballistic helmet, a tactical ballistic vest, ballistic leggings, a throat protector and a groin protector, and a gas mask and black tactical gloves.
TOM BEARDEN: The suspect was identified as 24-year-old James Holmes.
DAN OATES: We are not looking for any other suspects. We are confident that he acted alone. However, we will do a thorough investigation to be absolutely sure that that is the case, but, at this time, we are confident that he acted alone.
TOM BEARDEN: A man in Aurora who said he knows Holmes described someone quiet and unassuming.
MELVIN EVANS: He was laid-back, kept to himself, never really talked to anybody. The conversations we did have were very short. I mean, he was somebody you wouldn't even look at twice walking down the street, very, very mellow.
TOM BEARDEN: In short order, the night's terror shifted to Holmes' apartment four miles away. FBI agents and police attached a camera to a fire truck ladder to look inside, and discovered it was booby-trapped.
Police have evacuated a five-block area around the apartment complex. That's because they have discovered what the police chief described as sophisticated explosives. The FBI says that investigation could go on for days.
DAN OATES: We're not sure what we're dealing with in the home. They appear to be incendiary devices. There are some chemical elements there and there are also some incendiary elements. They're linked together with all kind of wires. As a layman, it's something I have never seen before. We have a lot of very smart bomb techs up there trying to figure out what we're going to do.
TOM BEARDEN: The search for a motive began almost immediately, but it appeared international terrorism wasn't involved.
JIM YACONE, FBI special agent: I want to emphasize, at this point, we do not see a nexus to terrorism, but we are continuing to look, and we are being as cautious as possible with the investigation as we move forward.
TOM BEARDEN: In San Diego, Calif., where Holmes' parents live, the family issued a statement saying their hearts go out to the victims.
LT. ANDRA BROWN, Police Department, San Diego, Calif.: As you can understand, the Holmes family is very upset about all of this. It's a tragic event and it's taken everyone by surprise. And they are definitely trying to work through this. They are cooperating with law enforcement. And they just ask your patience and diligence and respect at this time.
TOM BEARDEN: The shootings also spilled over to the presidential campaign, as both President Obama and Republican Mitt Romney called off their campaigning for the day.
The president spoke briefly to a crowd in Fort Myers, Fla., saying the country was united as one American family.
PRESIDENT BARACK OBAMA: And if there's anything to take away from this tragedy, it's the reminder that life is very fragile. Our time here is limited and it is precious.
And what matters at the end of the day is not the small things. It's not the trivial things which so often consume us and our daily lives. Ultimately, it's how we choose to treat one another and how we love one another.
TOM BEARDEN: Later, in Bow, N.H., Mitt Romney also expressed his condolences for those in Colorado.
MITT ROMNEY (R): Our hearts break for the victims and their families. We pray that the wounded will recover and that those who are grieving will know the nearness of God.
Today, we feel not only a sense of grief, but perhaps also of helplessness. But there is something we can do. We can offer comfort to someone near us who is suffering or heavy-laden. And we can mourn with those who mourn in Colorado.
TOM BEARDEN: Both men canceled scheduled campaign events today, and the campaigns said they would stop running ads in Colorado for now.