A nephew of fugitive Warren Jeffs has been jailed on contempt charges in Arizona — the sixth person connected to the exiled polygamist church leader to refuse to answer questions before a federal grand jury investigating Jeffs.

Benjamin Jeffs Nielsen, 25, was booked into the Central Arizona Detention Facility in Florence on July 14 by the U.S. Marshal's Service of Phoenix, prison officials confirmed Thursday.

Patrick Schneider, chief of the criminal investigations division for the U.S. Attorney's Office in Phoenix could not confirm that Nielsen was among those subpoenaed by federal authorities over the past seven months.

"We don't discuss any ongoing investigation and anything related to a grand jury is not a matter of public record," Schneider said.

It could not be immediately determined if Nielsen has an attorney.

Nielsen is a nephew of Jeffs, the leader of the Fundamentalist Church of Jesus Christ of Latter Day Saints, who is wanted in Utah and Arizona for alleged sexual misconduct for arranging marriages between underage girls and older men.

Since May, Jeffs has been on the FBI's Ten Most Wanted list, with a $100,000 reward offered for information leading to his capture.

Federal prosecutors in Arizona have been investigating Jeffs since at least January, when subpoenas were first served on a handful of Jeffs supporters at an FLDS meeting in Colorado City, Ariz., which with its twin border town of Hildale, Utah, is the home to most church members.

So far, six men including Nielsen have been charged with civil contempt of court for refusing to appear or answer questions before the grand jury. Grand jury proceedings are secret, so the scope of the investigation being conducted by federal prosecutors is unclear.

Among the others imprisoned in Florence are a Colorado City police officer, the town postal clerk, two local business men and Leroy Jeffs — Nielsen's father. All six could remain in prison until the grand jury's 18-month term ends next year.

Until recently, Benjamin Jeffs Nielsen had been living in Mancos, Colo., serving as the caretaker of a pair of properties owned there by David Allred, another close associate of Warren Jeffs.

Officials from both the Montezuma County, Colo., tax assessor's office and the sheriff's office said they knew Nielsen — although they said he initially gave them a different last name or identified himself as "just Ben" — and knew he was living there.

Deputy assessor Scott Davis said it is unknown how many people may be living on the Mancos properties. Both parcels had only one home a piece when purchased, but several other large homes had been constructed in both locations. The properties are fenced with a locked gate, Davis said.

Both Davis and Sheriff's Lt. Steve Harmon said it had been several months since they had seen Nielsen and they were unaware that he had been incarcerated.