Dr. George Tiller, 67, was serving as an usher during morning services Sunday when he was shot in the foyer of Reformation Lutheran Church in Wichita, Kansas, police said. The gunman fired one shot at Tiller and threatened two other people who tried to stop him.
The suspect, identified by one law enforcement agency as Scott Roeder, was taken into custody some 170 miles away in a Kansas City suburb about three hours after the shooting.
Roeder's ex-wife - who did not want her face shown - says he was obsessed with fighting abortion, reports CBS News correspondent Jeff Glor.
"I think he thinks he's right," she told Glor. "And that he was justified in doing what he's done."
His brother, David Roeder, told The Topeka Capital-Journal the family is "shocked, horrified and filled with sadness at the death of Dr. Tiller" and the possible involvement of their relative.
He called his sibling "kind and loving," but said he suffered from mental illness at times in his life.
"None of us ever saw Scott as a person capable of or willing to take another person's life," David Roeder said.
Tiller had been a lightning rod for abortion opponents for decades. The women's clinic he ran is one of three in the United States where abortions are performed after the 21st week of pregnancy, when the fetus is considered viable, and has been the site of repeated protests for about two decades.
A protester shot Tiller in both arms in 1993, and his clinic was bombed in 1985.
The threat against Tiller was so constant that his clinic had fortress-like security - around the clock guards and surveillance cameras, reports Glor. When he left, he often traveled with a bodyguard, in a bulletproof vehicle.
Sedgwick County District Attorney Nola Foulston indicated that charges against Scott Roeder will not be filed Monday. Foulston noted that the state has 48 hours to charge anyone who is in custody and said she planned to take the full two days to decide. She said any charges would be filed in state court.
Also, a law enforcement official said investigators have searched two homes as part of the inquiry into Tiller's killing. The official, who spoke on condition of anonymity because he was not authorized to discuss the investigation, said the homes are in Merriam, Kansas, and directly across the border in Kansas City, Missouri.
Roeder's former wife, Lindsey Roeder, said he had lived at a house in Merriam but moved out months ago.
Roeder, 51, was returned to Wichita and was being held without bail on one count of first-degree murder and two counts of aggravated assault.
Outside the clinic, flowers were placed along a fence, and the anti-abortion group Kansas Coalition for Life left a sign saying members had prayed for Tiller's change of heart, "not his murder."
In Washington, the U.S. Marshals Service said that as a result of Tiller's shooting, Attorney General Eric Holder had ordered it to "increase security for a number of individuals and facilities." It gave no details.
Tiller himself last had protection from the U.S. marshals in 2001. He and other doctors received such protection at different times in the 1990s.
A man with the same name as the suspect has a criminal record and a background of anti-abortion postings on sympathetic Web sites. In one post written in 2007 on the Web site for the militant anti-abortion group Operation Rescue, a man identifying himself as Scott Roeder asked if anyone had thought of attending Tiller's church to ask the doctor and other worshippers about his work. "Doesn't seem like it would hurt anything but bring more attention to Tiller," the post said.
But police said all early indications showed the shooter acted alone.
Operation Rescue condemned the killing as vigilantism and "a cowardly act," and the group's president, Troy Newman, said Roeder "has never been a member, contributor or volunteer." He may have posted to the organization's open Internet blog, Newman said, but so have thousands of nonmembers.
Operation Rescue founder Randall Terry, whose protests have often targeted Tiller, called the slain doctor "a mass murderer," adding: "He was an evil man - his hands were covered with blood."
In 1996, a 38-year-old man named Scott Roeder was charged in Topeka with criminal use of explosives for having bomb components in his car trunk and sentenced to 2 years of probation. However, his conviction was overturned on appeal the next year after a higher court said evidence against Roeder was seized by law enforcement officers during an illegal search of his car.
At the time, police said the FBI had identified Roeder as a member of the anti-government Freemen group, an organization that kept the FBI at bay in Jordan, Montana, for almost three months in 1995-96. Authorities would not immediately confirm if their suspect was the same man.
Morris Wilson, a commander of the Kansas Unorganized Citizens Militia in the mid-1990s, told The Kansas City Star he knew Roeder fairly well.
"I'd say he's a good ol' boy, except he was just so fanatic about abortion," Wilson said. "He was always talking about how awful abortion was. But there's a lot of people who think abortion is awful."
The slaying quickly brought condemnation from both anti-abortion and abortion-rights groups, as well as President Barack Obama.
"However profound our differences as Americans over difficult issues such as abortion, they cannot be resolved by heinous acts of violence," Obama said in a statement.
Wichita Deputy Police Chief Tom Stolz said Tiller apparently did not have a bodyguard with him in church, although the doctor was routinely accompanied by one. An attorney for Tiller, Dan Monnat, said the doctor's wife, Jeanne, was in the choir at the time of the shooting.
Monnat said in early May that Tiller had asked federal prosecutors to step up investigations of vandalism and other threats against the clinic out of fear that the incidents were increasing and that Tiller's safety was in jeopardy.
The last U.S. killing of an abortion doctor was in October 1998 when Dr. Barnett Slepian was fatally shot in his home in a suburb of Buffalo, New York. A militant abortion opponent was convicted of the murder.
One of Tiller's lawyers and friends, Dan Monnat, told CBS' The Early Show that Tiller had been supported by his wife and children in his decision to continue providing abortion services.
"If Dr. Tiller is not going to service a woman's right to chose, who will do it?" Monnat said.
"Many of those have been terrorized and run off by protesters," he said about other abortion providers.