More than 18 months after a Wichita, Kan., abortion doctor was gunned down in his church, a federal investigation into a possible conspiracy continues in Kansas City, Kan.

Federal agents have questioned more people in the past few weeks, while a grand jury convened after the murder of George Tiller is still under way.

The focus, according to those who have been interviewed, still appears to be on a Bible study group that Tiller’s killer attended.

At the same time, abortion-rights advocates are concerned that a recent North Carolina case signals an escalation in the threat of clinic-related violence.

Tiller was shot to death in May 2009 in the foyer of his Wichita church while serving as an usher. Scott Roeder of Kansas City was convicted of first-degree murder and sentenced to life in prison with no chance of parole for 50 years.

David Lloyd, a Warrensburg, Mo., attorney who used to attend Roeder’s Bible study group, said an FBI agent called him at the end of November.

“I think they’re just barking up the wrong tree,” Lloyd said. “None of us were involved in any kind of vast conspiracy or whatever it is they’re looking for.”

In October, two of Roeder’s former roommates who were members of the Bible study group told The Kansas City Star that they and several other members had testified before the grand jury in late September. The questions they were asked, they said, focused on whether Roeder had acted alone.

More of Roeder’s former associates say they have been contacted by authorities since then, including two additional members of the Bible study. The group met in members’ homes on Saturdays. Those attending described themselves as Messianic Jews who, unlike mainstream Jews, believe that Jesus was the Messiah.

“They’ve interviewed me at least nine times,” said Roeder’s former roommate, who led the study sessions at their house and testified before the grand jury in September. He asked that his name not be disclosed for fear of repercussion.

“There wasn’t any conspiracy within the Bible study group,” he said. “We were not part of this pro-life movement. We were never involved in that.”

After Tiller’s death, the Department of Justice announced it was looking into possible federal charges against Roeder, including a violation of the Freedom of Access to Clinic Entrances Act, which was signed into law in 1994 to prevent clinic violence. Federal investigators also said they were looking into whether anyone else played a role in Tiller’s death.

Abortion-rights advocates have been pressing the Justice Department to investigate the possible existence of a network of anti-abortion extremists involved in clinic-related violence, including the murder of Tiller. They point to the recent case of a North Carolina activist as a reason for concern.

In November, Justin Carl Moose signed a plea bargain with federal prosecutors on charges of distributing information on manufacturing and using an explosive.

According to court documents, Moose provided detailed information and instructions on explosives to a person he thought was going to bomb a North Carolina abortion clinic. That person actually was a confidential informant.

Moose told the informant that he was a member of the Army of God, a name associated with an underground network of anti-abortion extremists.

“I have set up groups,” the informant said Moose told him. “I have trained people and this is not my first rodeo.”

Authorities said Moose also used his Facebook page to advocate violence against abortion clinics and their employees and posted instructions on how to make explosives. One Facebook post, according to court documents, said, “End abortion by any means necessary and at any cost. Save a life, shoot an abortionist.”

Soon after Moose was charged, Justice Department investigators showed up in Kansas City to conduct more interviews on the Roeder case. So far, none of Roeder’s supporters — many of whom vocally support the killing of abortion doctors as an act of justifiable homicide — have been subpoenaed by the grand jury.

The Justice Department has remained tight-lipped.

“Our investigation remains ongoing,” said spokeswoman Xochitl Hinojosa. She declined further comment.

This isn’t the first federal investigation into a possible conspiracy of abortion clinic violence. In 1994, then-Attorney General Janet Reno called for an investigation, and a federal grand jury in Alexandria, Va., subpoenaed abortion foes around the country.

The investigation focused on about three dozen activists who advocated killing abortion doctors, including several from the Kansas City area. Many of those who were subpoenaed by that grand jury are now supporters of Roeder.

The grand jury disbanded in 1996 without finding evidence of a nationwide conspiracy.

Kathy Spillar, executive vice president of the Feminist Majority Foundation, said Moose’s case and other recent incidents indicate that the situation is escalating.

“Moose is with the Army of God,” Spillar said. “You’ve got an intersection of Army of God elements purported to have been talking with other anti-abortion leaders, and this intensified targeting and stalking of doctors. It points to how critical this federal investigation is.”

Roeder’s supporters, however, call the investigation a witch hunt and say there’s nothing to uncover.

“Despite the tremendous budget devoted to building any kind of case possible, and especially how rare it is that there is even an illegal action any more, (another grand jury) reminds me of Chicken Little with his warning that the sky is falling,” said Dave Leach, an Iowa anti-abortion activist and friend of Roeder.

The Rev. Donald Spitz, director of Pro-Life Virginia, who operates the Army of God website, said he recently discussed the grand jury investigation with Roeder.

“He assures me there’s nothing there,” Spitz said. “And I agree. I think Scott would know better than to involve others.”