Beth Stubbs got engaged on her 15th birthday. Her future husband — very future, she would explain later — Orson William Black Jr., was 37. He already had a legal wife and other women in his plural family along the Utah-Arizona line.

That day, Stubbs and Black talked about having children. Stubbs would later tell investigators Black handed her a little book. She said the book instructed her on how to artificially impregnate herself with Black’s semen.

“Did he tell you why he did not want to have regular sex to have kids?” an investigator from the Arizona Attorney General’s Office asked three years later.

“So we wouldn’t get in trouble,” Stubbs replied.

New documents provided by the attorney general’s office elaborate on the investigation into the polygamist Black that led to prosecutors charging him with four felony counts of sex with a minor in February 2003.

Black and his big family fled. Over the next 14½ years, local, state and federal law enforcement in Utah, Arizona and Mexico pursued him

Black’s story took another strange turn in September 2017. A Mexican drug cartel killed three people living with Black on a ranch in Chihuahua, according to that state’s attorney general and Mexican news outlets.

In this photo provided with a redaction by the law enforcement in the Mexican state of Chihuahua, Orson William Black, 56, stands while being detained Nov. 5, 2017. Black is a former member of the polygamous Fundamentalist Church of Jesus Christ of Latter-Day Saints who has been on the run from child sex abuse charges in Arizona since 2003. Courtesy Photo.

Mexican authorities arrested Black on Nov. 5, taking him to a detention center in El Paso, Texas, but he was released later that month.

Why would Arizona authorities hunt for him for so long, only to let him go? It turns out the Arizona attorney general had quietly dropped the charges against Black six months earlier.

Black did not return messages seeking comment last week.

The records, provided to The Salt Lake Tribune under a public records request, show that the best evidence that Black had sex with teenagers was that those teens became pregnant. However, Stubbs and her sister, Roberta Stubbs, who moved in with Black at age 16 and soon was expecting, had explanations.

Both said they artificially inseminated themselves with a syringe Black gave them.

“He gave it to me when we were alone,” Roberta Stubbs said, according to a transcript of her 2002 interview with an investigator. “And I went to my room just before going to bed and sat on the edge of my bed and put it in. I put the syringe in my drawer and went to bed. The next day I gave it back to him and that’s it.”

Roberta Stubbs had two children through artificial insemination while Beth Stubbs had one miscarriage and one live birth, according to documents. The sisters said they had never had any sexual contact with Black.

They weren’t the only ones telling the insemination story. A woman, who called Black her boyfriend, said the three children she had with him were conceived that way, too. Black’s legal wife, Amy Black, said she saw the syringe the Stubbs sisters used, according to interview transcripts.

Despite all that, then-Arizona Attorney General Terry Goddard filed the sex-with-a-minor charges against Black.

Todd MacFarlane, an attorney who used to represent Black and the women and girls who lived with him, said the Arizona attorney general never had any evidence underage girls conceived through sex with Black. He assumes that had the case gone to trial, prosecutors would have argued the story of artificial insemination was too fanciful to be true.

“Despite the complete lack of any evidence to the contrary,” MacFarlane said in an interview Tuesday, “they just didn’t want to believe that’s what happened.”

The documents also show how Black worked to have a plural family without violating the law in Utah or Arizona.

Black and his other partners referred to their relationships as a “spiritual engagement.”

“It’s a promise that he’ll marry me in the afterlife,” Beth Stubbs explained in her interview with investigators.

The spiritual fiancees appear to have lived with Black the same way plural wives live with a husband. But calling themselves engaged rather than married might have insulated Black and his partners from bigamy prosecutions.

“He was trying to figure out,” MacFarlane said, “how to legally navigate the whole plural marriage minefield, if you want to call it that, including the underage issue.”

Black was a member of the polygamous Fundamentalist Church of Jesus Christ of Latter-Day Saints but split from that group in the 1980s. He continued living in the FLDS’ longtime home of Colorado City, Ariz. The documents recount how attorney general investigators and local sheriff’s deputies surveilled Black’s home, trying to apprehend him after the charges were filed in winter 2003.

Black escaped to Mexico. For years, authorities in Arizona and Mexico received tips that Black may have been in Sonora or Chihuahua, documents show. A wanted poster listed Black and seven wives he may have been traveling with, including those women who referred to Black as their boyfriend or fiance.

The slayings at his ranch in Chihuahua appear to have lead to his arrest.

Someone examines a travel trailer In this photo provided by the law enforcement in the Mexican state of Chihuahua, Orson William Black, 56, was arrested in Chihuahua Nov. 5, 2017. Black is a former member of the polygamous Fundamentalist Church of Jesus Christ of Latter-Day Saints who has been on the run from child sex abuse charges in Arizona since 2003. Courtesy Photo.

One of the three people killed was Robert William Black. He was one of the children born in 1998 that law enforcement suspected of being conceived through unlawful sex.

After Black was released from federal custody in November, then-Arizona attorney general spokeswoman Mia Garcia told The Associated Press the office had decided it didn’t have enough evidence to pursue the sex-with-a-minor charges.

“We needed the girls to testify or in some way help us with the evidence,” Garcia said.

Goddard, the former Arizona attorney general, told The Associated Press that he lamented Black would not be prosecuted.

“If somebody can just skip the country and then avoid what I believe was a very legitimate child molestation rap, that’s a very sad development,” Goddard said.

The Arizona Attorney General’s Office appears to have tried one more time at proving a case against Black.

The records show how in January of this year, investigators traveled to Colorado City and adjoining Hildale, Utah, searching for the Black family. An investigator’s report says they got Beth and Roberta Stubbs on the phone. Both declined to speak without an attorney present. There’s no indication from the records such interviews have occured.