WICHITA, Kansas (CNN) -- Scott Roeder's ex-wife said she believes her former spouse was capable of murder.
Scott Roeder, 51, is being held on a first-degree murder charge and two counts of aggravated assault.
Roeder, 51, is sitting in a Kansas jail, charged with murdering George Tiller, one of the few U.S. doctors who performed late-term abortion.
"He was determined that if the abortion doctor killed the baby, then he didn't have any right to live either," Roeder's ex-wife Lindsey Roeder told reporters on Monday, refusing to show her face to cameras.
Lindsey Roeder said their 10-year marriage ended 13 years ago in part because he had a fanatical preoccupation with certain views, including those on abortion.
She said her ex-husband believed killing an abortion provider "is justifiable," and described him as self-righteous and someone who may be capable of murder.
Scott Roeder was charged Tuesday with one count of first-degree murder and two counts of aggravated assault stemming from Tiller's shooting death at Tiller's Wichita church Sunday morning. Watch panel discuss ramifications of slaying »
During a brief initial court appearance, in which he appeared via video from the county jail, Roeder requested a court-appointed lawyer. He has made no plea, and a preliminary hearing is scheduled for June 16.
Police have not disclosed a possible motive in Tiller's killing. But associates have told CNN that Roeder was a regular among the anti-abortion protesters who routinely gathered at Tiller's Wichita clinic, Women's Health Care Services.
And records and interviews with family and fellow abortion protesters suggest Roeder had a fanatical preoccupation with abortion and used Christianity to support his beliefs.
In 1996, he was arrested in Topeka, Kansas, with explosives, a military rifle, ammunition and a gas mask in his car, according to records.
His ex-wife said that at that time he intended to blow up an abortion clinic.
A Shawnee County judge called Roeder a "substantial threat to public safety" telling him that one must follow the law as established, not the law as one might wish it to be.
Roeder pleaded not guilty, spent 16 months in prison and eight on probation. But his lawyer argued on appeal that his car had been illegally searched, and Roeder's conviction was vacated.
He became known as a regular at protests outside abortion clinics, say those who rallied alongside him. Anti-abortion activists Anthony Leake and Regina Dinwiddie told CNN that Tiller had strong beliefs.
"He was a confessing Christian," Leake continued. "He always had his Bible, which wasn't uncommon. He professed faith in Jesus Christ."
A man named Scott Roeder signed a message on the anti-abortion group Operation Rescue's Web site in 2007, calling for prayers to shut down Tiller's "death camp."
"Sometime soon, would it be feasible to organize as many people as possible to attend Tillers church (inside, not just outside) to have much more of a presence and possibly ask questions of the pastor, deacons, elders and members while there? Doesn't seem like it would hurt anything but bring more attention to Tiller," the message reads.
National anti-abortion organizations, including Operation Rescue, condemned Tiller's slaying. "[The alleged killer] is not one of us, and if he thinks he is, then he is deluded," said the Rev. Gary Cass, the director of the Christian Anti-Defamation Commission.
Dinwiddie, a 54-year-old grandmother, said Roeder once told her that he confronted a doctor at a Planned Parenthood center, telling the physician, "Now I know what you look like."
"We all said, 'Scott, you better leave or they are gonna get after you,' " Dinwiddie said. "Next thing, all these people come rushing out of the place, all worried. Scott was standing up for what he believed in."
In the mid-1990s, police said he was also possibly linked to the Freemen, an anti-government group based in Montana.
Eugene Frye, who says he has known Roeder for years as an anti-tax campaigner, said just Roeder showed up at a recent abortion protest talking about this year's trial of Tiller, whom Frye called the "killer." Tiller was acquitted in March of 19 misdemeanor counts of performing unlawful procedures at his clinic, and Frye said Roeder told him he had attended the trial. See what people are saying about Tiller's slaying »
"He just said he'd been down there, and that the trial was a sham," Frye said. But he said he was surprised that Roeder was a suspect in Tiller's death, saying he never spoke of any kind of violence. Tiller describes the philosophy of his clinic in 1999 »
CNN's Ed Lavandera, Randi Kaye, Paul Vercammen and Ashley Fantz contributed to this report.