(CNN) Two civilians and a police officer were killed when a gunman opened fire at a Colorado Planned Parenthood clinic in a nearly six-hour standoff Friday.

The suspected gunman is Robert Lewis Dear, 59, a law enforcement official told CNN. The official did not provide additional information.

Police captured him, but they're still working to pinpoint his motive -- and make sure he didn't leave any explosives inside or outside the Colorado Springs building.

Bomb technicians are investigating what's believed to be the suspect's vehicle in a parking lot, a law enforcement official said.

It was not immediately clear why Planned Parenthood was the target of the shooting.

One Planned Parenthood official said the motive behind the attack was unknown, but pointed to what she called a "poisonous environment that feeds domestic terrorism" as a possible cause.

Photos: Shootout in Colorado Springs Photos: Shootout in Colorado Springs A suspect is in custody on Friday, November 27, in Colorado Springs, Colorado. Police were in a shootout with a gunman inside a Planned Parenthood facility, hours after a shooter was first reported in the area. Hide Caption 1 of 19 Photos: Shootout in Colorado Springs People in the building across from Planned Parenthood in Colorado Springs start to emerge from hiding. Hide Caption 2 of 19 Photos: Shootout in Colorado Springs A bus of evacuees make its way towards neighboring hospitals. Hide Caption 3 of 19 Photos: Shootout in Colorado Springs Colorado Springs Fire Department Chief Christopher Riley, center, takes questions from the media. Hide Caption 4 of 19 Photos: Shootout in Colorado Springs An unidentified victim is transported to an ambulance. Hide Caption 5 of 19 Photos: Shootout in Colorado Springs People are helped to safety. It was not immediately clear at the time of the attack whether Planned Parenthood was the target of the shooting. Hide Caption 6 of 19 Photos: Shootout in Colorado Springs An officer waits at an intersection near the scene of a shooting. Hide Caption 7 of 19 Photos: Shootout in Colorado Springs A woman is escorted to an ambulance by police near the scene. Hide Caption 8 of 19 Photos: Shootout in Colorado Springs Police sit on the roof of a Chase Bank branch across the parking lot from the scene at Fillmore Street and Centennial Boulevard. Hide Caption 9 of 19 Photos: Shootout in Colorado Springs Colorado Springs Police Lt. Catherine Buckley addresses the media during the incident. Eleven people have been transported to local hospitals, she said. Five are police officers from various responding agencies. Hide Caption 10 of 19 Photos: Shootout in Colorado Springs Colorado Springs rescue personnel stand ready near the scene. Hide Caption 11 of 19 Photos: Shootout in Colorado Springs People are escorted to an ambulance during the standoff. Hide Caption 12 of 19 Photos: Shootout in Colorado Springs A police officer stands guard. Hide Caption 13 of 19 Photos: Shootout in Colorado Springs Rescued people are escorted from the area by emergency personnel. Hide Caption 14 of 19 Photos: Shootout in Colorado Springs The shooting, first reported around 11:30 a.m. (1:30 p.m. ET), left a nearby shopping center on lockdown as police searched for the gunman. Hide Caption 15 of 19 Photos: Shootout in Colorado Springs An officer patrols the perimeter. Denise Speller, who works at a nearby salon, said she heard at least 10 gunshots go off and saw a police officer get hit. Hide Caption 16 of 19 Photos: Shootout in Colorado Springs It was not immediately clear whether Planned Parenthood was the target of the shooting. Police said the original 911 call came from the building. Hide Caption 17 of 19 Photos: Shootout in Colorado Springs Police officers respond to the scene. Hide Caption 18 of 19 Photos: Shootout in Colorado Springs Colorado Springs police officers search the area near the scene. Hide Caption 19 of 19

"We don't yet know the full circumstances and motives behind this criminal action, and we don't yet know if Planned Parenthood was in fact the target of this attack," Vicki Cowart, president and CEO of Planned Parenthood of the Rocky Mountains, said in a written statement. "We share the concerns of many Americans that extremists are creating a poisonous environment that feeds domestic terrorism in this country. We will never back away from providing care in a safe, supportive environment that millions of people rely on and trust."

Cowart told CNN she believes all staff and patients from the clinic are accounted for.

"We're still reaching out to confirm individuals, how they are. I believe no one of our staff was severely injured. I also believe at this time that none of our patients were injured," she told CNN.

Officer was a six-year veteran

The slain officer, 44-year-old Garrett Swasey, worked for the University of Colorado in Colorado Springs and was on campus about 10 miles away when the shooting broke out. He went to the scene "in support of an officer under fire," the school's chancellor said in a statement.

Officer Garrett Swasey was killed in Friday's Planned Parenthood shooting.

Swasey was a six-year veteran of the university's police force.

Four civilians and five police officers were taken to hospitals with gunshot wounds. The injured victims were in good condition Friday night, police Lt. Catherine Buckley said.

"The officers, they're obviously in some pain, but thankfully they're alive and talking to us, and they're heroes ... The courage they displayed today saved many, many lives -- no doubt," Colorado Springs Fire Chief Christopher Riley said.

In a statement released late Friday, Planned Parenthood CEO Cecile Richards thanked law enforcement officers.

"Our hearts go out to the families and loved ones of the brave law enforcement officers who put themselves in harm's way in Colorado Springs," she said.

The Planned Parenthood family grieves for Officer Garrett Swasey's family, friends and colleagues dealing with heartbreaking loss tonight. — Cecile Richards (@CecileRichards) November 28, 2015

Siege lasted for hours

The announcement of the suspect's arrest came nearly six hours after someone first called 911 around 11:30 a.m. (1:30 p.m. ET) and reported a shooter was inside the Planned Parenthood building, which is near a shopping center and numerous offices.

For hours, police reported shootouts with the gunman, warning people to stay inside nearby businesses and seek shelter.

The shooting brought life to a standstill as police closed roads and people were trapped inside businesses for hours in a busy corner of the central Colorado city, which has more than 400,000 residents.

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First, Tessa Smart saw a look of concern flash across a patient's face in a nearby chiropractor's office where she works. Then she heard the gunfire.

"I heard a bullet go right by the door and hit something," she told CNN. "And I ran back to my desk and grabbed a bunch of keys and fumbled at the door trying to find one to lock it. ... As I was doing that I was seeing the police commotion outside, police running everywhere, ducking behind cars with guns."

Denise Speller, who works at a salon, said she heard at least 10 gunshots go off and saw a police officer get hit.

"It was terrifying," she said.

Joan Motolinia said he got a phone call Friday afternoon from his sister, who was inside the clinic.

"I heard the shooting," he said, choking up as he described the situation to reporters. "She couldn't say too much because she was afraid."

In a nearby grocery store, an announcement over the intercom told shoppers they weren't allowed to leave. They huddled with staff at the back of the supermarket.

It was shocking to watch SWAT teams while holed up inside a nail salon, witness Jill Lavelle said.

"Seeing the SWAT members squatting down in their shields and their riot gear, with their automatic rifles out, that was very ... I never have experienced anything like that before," she said.

Despite initial fears that the shooter could be on the loose outside, authorities now believe he remained inside the Planned Parenthood building throughout the siege, Buckley said.

Several injured victims made their way into a nearby bank, she said.

Attack comes as Planned Parenthood faces criticism

Hours after the shooting began, video from CNN affiliates showed people in medical scrubs and white coats being escorted from the scene.

Planned Parenthood is a national health care provider that delivers reproductive health care and sex education to women and men throughout the United States. The organization runs nearly 700 health centers throughout the United States, according to its website.

The group says each year 2.7 million people in the United States visit its health centers for health care services and information. Abortion is among the services Planned Parenthood clinics provide, an issue that's made the organization a target in the past.

It's faced sharp criticism in Washington and from some Republican presidential candidates on the campaign trail after an anti-abortion group released a series of videos alleging that Planned Parenthood engaged in the selling of fetal organs and parts for profit.

Planned Parenthood has strongly disputed the videos and contended the tapes provide a distorted account because they are heavily edited.

At least three Planned Parenthood buildings have been vandalized since September.