"Every doctor who performs abortions is on the list," said Dr. Warren Hern about the names of doctors willing to perform the procedure he says anti-abortionist groups track and publicize.

Hern's Boulder Abortion Clinic has been specializing in late-term abortions since it was founded in 1975.

"I'm appalled and shocked by this assassination, but I'm not surprised," Hern said of Tiller's death. "This is not the single act of a deranged gunman. This is the absolutely predictable result of 35 years of anti-abortion harassment."

"Tiller's death is what they want to happen," said Hern, who declined to specify on the degree to which security at his clinic has been ramped up since Tiller's murder on Sunday.

Sarah Huntley, a spokeswoman for the Boulder Police Department, said that there have been an increased number of patrol cars sent to monitor the areas near Hern's house and clinic since Tiller's death.

But perhaps more telling, said Huntley, is that most of the security responsibilities concerning Hern and his staff have been handed over to the U.S. Marshall Service, a move she deems "unusual."

A spokesman for the U.S. Marshall Service told ABCNews.com that it is against their policy to comment on protective details.

Scott Roeder, the man accused of shooting Tiller in church, is expected to be charged today with homicide.

Roeder, 51, has a history of being one of the most outspoken anti-abortion militants in the country, according to the Southern Poverty Law Center, an organization that tracks supremacist and hate groups. One of the groups that the SPLC kept an eye on was the anti-government Freemen movement, of which Roeder was a member.

"[Roeder] wanted to do something about abortion," said Morris Wilson, who was close with Roeder during the late 1990s when both men were associated with the Freemen movement.

"He was determined," said Wilson. "He made me nervous because he was just so, so radical."

In 1996, Roeder was charged in Topeka with criminal use of explosives for having bomb components in his car trunk and sentenced to 24 months 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 Freemen, which had kept the FBI at bay in Jordan, Mont., for almost three months in 1995-'96.

Heidi Beirich, a spokeswoman for the SPLC, said that the Freeman movement has been dormant in recent years and that the group has not been categorized as a functioning group since the late 1990s.

"The Freemen has its heyday in the 1990s," she said. "They were an extreme anti-government group that did not believe for example that the government had the right to decide what people should do in terms of guns or taxes."

Tiller's lawyer and friend, Lee Thompson, told "Good Morning America" today that Tiller, 67, was "one of the most positive and courageous men I've ever known."