ELDORADO, Texas - The first polygamist sect member to face criminal trial following last year's raid at the Yearning For Zion Ranch in West Texas was convicted Thursday of sexually assaulting an underage girl with whom he had a so-called "spiritual marriage." Raymond Jessop, 38, didn't visibly react when the verdict was read after just more than two hours of jury deliberations. Free on bond during trial, he was immediately handcuffed and led to jail. Jurors were expected to return to court Monday to begin deciding his sentence on the child sexual assault conviction. He faces up to 20 years in prison.

Lawyers in the case declined to comment on the verdict Thursday.

Jessop allegedly has nine wives. He also faces a bigamy charge, but that case is to be tried later. The girl in the assault case, now 21, was previously in a spiritual marriage with Jessop's brother before being "reassigned" to Jessop when she was 15, according to documents seized at the ranch. She became pregnant at age 16.

During closing arguments, Assistant Attorney General Eric Nichols stood before photos of the young mother and toddler in prairie dresses.

"There is a sound foundation based not just in documents -- based in DNA evidence for which the documents serve as corroboration ... that Raymond Merril Jessop behind those gates, behind that guard house, behind those walls, sexually assaulted" the then-teen, he said.

Forensic experts who testified during the trial, which began with the largest jury pool in the small county's histol, 12 FLDS men have been indicted on charges ranging from failure to report child abuse to sexual assault since authorities raided the ranch last year. The 439 children taken from the property and placed in foster care following the raid all have been returned to their parents or other relatives.

Jeffs, revered by the FLDS as the group's prophet, was convicted in Utah as an accomplice to rape. He awaits trial in Arizona on charges related to underage marriages there. He'll then face separate sexual assault and bigamy charges in Texas.

The FLDS is a breakaway sect of the mainstream Mormon church, which renounced polygamy more than a century ago and does not recognize the FLDS.

Historically based around the Arizona-Utah state line, the FLDS bought a ranch about 150 miles northwest of San Antonio, in Eldorado, six years ago, and began building massive log homes and a towering temple.

The raid of the insular group made national headlines as women in prairie dresses and braids were moved off the ranch, and child welfare officials took custody of their children in one of the largest custody cases in U.S. history. .