Criminal investigators in Texas have taken DNA samples from the jailed polygamist sect leader Warren Jeffs in an attempt to prove that he sexually assaulted four girls at the compound where more than 450 children were seized by the state’s Department of Child Protective Services (CPS).

News of the DNA samples came after the Texas Supreme Court upheld a ruling by the 3rd Court of Appeals that the CPS overstepped its authority in removing the children from the Yearning for Zion Ranch, operated by the Fundamentalist Church of Jesus Christ of Latter Day Saints (FLDS), and placing them in foster care.

Under a deal announced last night the CPS will begin returning the children to their families on Monday as long as the parents can show identification, agree to take parenting classes and remain in Texas.

Although the deal was made only between the CPS and the 38 mothers of the 124 children who filed the original complaint with the 3rd Court of Appeals, it will affect all of the families involved in the case.

Jerry Strickland, a spokesman for the Texas Attorney General’s office, said that the DNA samples were taken on Thursday at an Arizona jail where Jeffs awaits trial on charges of being an accomplice to incest and sexual conduct.

He was sentenced previously to prison in Utah as an accomplice to rape in arranging a marriage between a 14-year-old and 19-year-old. Jeffs is considered a prophet by the FLDS, which separated from the mainstream Mormon faith in the 1930s when the latter banned multiple marriages.

Investigators believe that Jeffs may have sexually assaulted four girls at the Yearning For Zion Ranch in January 2004 and July 2006. They have wedding photos and church records indicating that he had spiritual unions — marriages recognised by the FLDS but not the law — with four girls ranging in age from 12 to 14, according to an affidavit filed by Denis Gilbert, an Arizona police officer. At least one girl conceived a child at 15, the affidavit says. Under Texas law girls younger than 16 cannot consent to sex or marriage. Photographs of Jeffs are hung throughout the school at the ranch and alongside pictures of Joseph Smith, the founder of the Mormon Church.

The CPS raided the ranch on April 3 and took all the children who were living there, with officials claiming that girls were being “groomed” to accept sex with their middle-aged “spiritual husbands” as soon as they reached puberty, and that boys were being indoctrinated to perpetuate the cycle of abuse.

The case began to fall apart when several of the allegedly underage girls turned out to be older than first thought. Identification was made more difficult because many of the sect members are given the same names. Concerns then emerged that the original reason for the raid — a phone call to the authorities by an alleged victim — was a hoax. By May 22 the 3rd Court of Appeals had ruled that the CPS did not have enough evidence to remove the children, who are currently held in 16 locations across the state.

Members of the FLDS believe that plural marriage is a way to get to heaven. The mainstream Mormon Church now excommunicates members who engage in polygamy and reject any connection with the FLDS. The ranch was bought in 2003 and built by Jeffs as a home for church members who had fled attention by the media and the authorities in Utah and Arizona.

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