SALT LAKE CITY » The University of Utah is investigating a complaint that a convicted felon working at a fertility clinic replaced a customer’s sperm with his own, fathering a girl 21 years ago.

The mother of the girl, Pamela Branum, says she and her husband discovered a genetic mismatch in their daughter, and were able to trace her lineage with help from relatives of the now-deceased fertility clinic worker, Thomas Ray Lippert.

"I don’t think we’re the only ones," Branum told CBS affiliate KUTV in Salt Lake City. "We think we’re one of many" victims who used a clinic that was operated by faculty members.

The University of Utah says there is "credible" evidence of semen tampering or mislabeling. On Friday, the university announced it was opening a hotline and offering paternity testing to anyone who used the clinic between 1988 and 1993.

"It was hard at first, to think, ‘Who am I?’" the daughter told KUTV in San Antonio, where the family moved in 2003. "I thought I was this person (of) my mom and my dad. Now, my dad is not my biological father. Who am I?"

In a statement that stopped short of taking responsibility or naming Lippert, the University of Utah Health Care system says it appears Branum’s daughter was fathered by a clinic employee. The university says there are no remaining records from the Reproductive Medical Technologies clinic to prove the family’s claim, or any evidence of other cases.

Kathy Wilets, a spokeswoman for the university’s Health Sciences division, said she could not answer a series of questions submitted by The Associated Press in writing. She declined comment on what officials have learned since opening the investigation in April 2013.

"Truthfully, they haven’t been investigating," Branum told The Salt Lake Tribune. "They’ve been stonewalling this whole time."

The fertility clinic performed some university services and was located next to a university laboratory. Three of the clinic’s owners were faculty or staff members, the university statement says. Surviving members of the clinic refused comment to The Salt Lake Tribune.

A DNA test of Lippert’s 99-year-old mother confirmed that she was the daughter’s biological grandmother, professional genealogists have told Utah news outlets.

The family said they stumbled into their unhappy discovery while tracing their lineage using widely available DNA tests.

Branum said she didn’t need a sperm donor — and would not have taken Lippert’s — when she was impregnated with what she thought was her husband’s sperm in 1991.

"I can’t imagine a couple seeing him and saying ‘Yeah, I want him,’ she said.

In a widely publicized case in 1975, Lippert took a plea bargain on kidnapping and other charges for subjecting a Purdue University female student to electroshock behavioral modification techniques in a so-called "love experiment."

The Salt Lake Tribune said he served two years in prison. The AP wasn’t immediately able to retrieve court documents for the case.

The Branums, formerly of Park City, Utah, moved to San Antonio in 2003. John Branum is a retired Marine; his wife has two boys from a previous marriage.

Fertility clinics are supposed to follow industry standards to avoid mix-ups and comply with the U.S. Clinical Laboratory Improvement Act, said Eleanor Nicoll, a spokeswoman for the American Society for Reproductive Medicine.

"What happened in Utah isn’t the result of the clinic not complying with regulations. This is a criminal act," Nicoll said Monday. "He’s a bad actor."

Sperm mix-ups are nothing new, but many cases involve honest mistakes.

In what Nicoll called the most notorious case, Virginia fertility doctor Cecil Jacobson was convicted of fraud in 1992.

Jacobson tricked some patients into believing they were pregnant and lied to others when using his own sperm to inseminate them, fathering at least 15 of his patients’ children, authorities said.