Federal agents investigating a plot to kill Jesse Jackson are looking for links between violent white supremacist groups and the couple charged in the case, who reportedly claim to be "a lower rung" in the assassination conspiracy.

Londell Williams, 30, who is charged in the case along with his wife, Tammy, 27, told an informer that he was a low-level member of a group that was planning to kill the Democratic presidential candidate and had not been involved in planning the slaying, The New York Times reported Thursday.The couple, residents of Washington, Mo., were ordered held without bail Tuesday by U.S. Magistrate Carol Jackson pending grand jury action in the case.

They are charged in a federal complaint with conspiring to kill Jackson and possession of a fully automatic rifle not registered to them. The complaint said the AR-15 rifle was to be used in the assassination.

The charges are based in part on tape-recorded conversations in which Londell Williams is alleged to have claimed that the white supremacist group the Covenant, the Sword and the Arm of the Lord was plotting to kill Jackson because he was "getting too close to being president of the United States."

Officials said Londell Williams passed a lie detector test Tuesday in which he denied membership in the neo-Nazi group.

Federal officials are looking for links between the couple and the white supremacist group.

"We are seeking out every shred of evidence and talking to every person we can who might know something," said Rich Adams, a spokesman for the Secret Service.

An unidentified investigator said Williams told the informer "that he was kind of a lower rung of this organization, and he certainly wouldn't be involved in the planning of an assassination," the Times said.

Londell and Tammy Williams were being held at the St. Clair County jail in Belleville, Ill., which is used to house suspects in federal custody, said Jay Foushee, agent in charge of the Secret Service's office in St. Louis.

Court records show Londell Williams was on probation in Christian County, Mo., from convictions for possession of hallucinogenic mushrooms, unlawful use of a weapon and probation revocation, court records showed. Tammy Williams was on probation from convictions for petty theft, possession of drugs and possession of paraphernalia, the records showed.

At an appearance Tuesday night in Los Angeles, Jackson said the reports of the conspiracy would not affect his campaign.

"I will not lower our tone nor will I surrender. Our campaign will continue against the odds," he said.

An informant who was a neighbor of the couple told the Franklin County sheriff's department May 9 that the couple was conspiring to kill Jackson, the federal complaint said. The sheriff's office contacted the Secret Service, which began an investigation.

The informant, equipped with a hidden microphone, met a day later with Londell Williams, the complaint said. The carpenter told the informant he was a member of the Order and other white supremacist groups.

A map in a bag with the rifle was found by the Secret Service lab in Washington, D.C., to have an identifiable fingerprint shown to be that of Londell Williams, the complaint said.