When Joseph Laedtke got the results of his ancestry DNA test in December 2024, he was shocked to learn he had nine half-siblings. And that they all seemed to trace back to his mother’s former doctor.

Mary Ellen Lukezich and her late husband, Thomas Laedtke, went to see Dr. Frederick Dettmann in the early 1980s when they were struggling to have a child, she said. The Wisconsin couple spent two years undergoing fertility treatments and eventually agreed to undergo artificial insemination using donor sperm.

She remembered that Dettmann suggested using donor sperm from a medical student. Lukezich told NBC News that she was assured upon asking questions of Dettmann that the donor was unlikely to donate again, that he was from out of state and that he was chosen to closely match her and her husband’s appearance.

“I was young,” Lukezich said. “I so wanted to be a mom that I was going to do anything, and I did whatever he asked me to do.”

She and her husband kept the decision to use donor sperm private, she said.

“This was our personal road, and no one needed to know. I got pregnant, everyone was happy, and that was the end of the story,” she said. “It was great. I tried again, but I never got pregnant again.”

It wasn’t until her now 43-year-old son submitted his DNA to a genetic testing company that she learned her doctor may have used his own sperm to inseminate her.

Laedtke said that when he submitted the test around November 2024, he wasn’t expecting the results to yield anything surprising.

“I got an email from Ancestry, which is the company that I ordered the DNA test from, that I had a half-sister,” Laedtke said. “And so when I went into my DNA results and the relationships, I had noticed that there was multiple half-siblings that it had suggested that I was related to.”

He called his mom right away and learned for the first time that his parents used donor sperm to conceive him. Lukezich was shocked, however, to learn from her son that his ancestry results suggested Dettmann was the donor.

Laedtke said he made the connection to Dettmann using genealogy tools available through Ancestry. He remembered his mother screaming on the phone when he revealed the information to her.

At first, Laedtke wished that the man who raised him, who died in 2005, was there to be with them through the ordeal. And then, as he began to realize the extent of the situation, Laedtke said, he felt “disgust and disappointment.”

“What he did was incomprehensible, and it was such a betrayal of trust that I just want to make sure that if I have the opportunity to hold him accountable for the pain that he caused my mom and the things that he put her through that maybe she didn’t even know at the time,” he said.

Lukezich said learning what her doctor is alleged to have done now feels violating.

“I feel like I’ve been raped,” she said. “And it’s not right. And I want other women to feel OK about coming forward with this.”

Al Foeckler, their attorney, says multiple women have contacted him since Laedtke and Lukezich went public with their situation to share their own uncomfortable interactions with Dettmann dating as far back as the 1970s.

“There is no question in my mind that this man was a serial predator of women,” Foeckler told NBC News.

Dettmann, 91, retired from his practice in the 1990s and lives in Arizona.

A lawyer for Dettmann did not immediately respond to an emailed request for comment. In a statement to the Milwaukee Journal Sentinel, attorney Sean Gaynor said Dettmann is aware of the allegations but is unable to speak about patient care because of privacy laws.

“The events referenced are alleged to have occurred almost 50 years ago,” Gaynor said. “Dr. Dettmann has no independent recollection of the individuals making these allegations and is unaware of any evidence supporting the claims being asserted.”

A report was filed in 1985 when a man told police that Dettmann assaulted his wife during a gynecological exam, according to the Whitefish Bay Police Department in Wisconsin.

Dettmann denied the allegation, and authorities declined to pursue charges, because the burden of proof was “too difficult.”

No other information was provided, and the alleged victim’s name was redacted. Whitefish Bay Police Chief Patrick Whitaker told NBC News that all other records about the case would have been destroyed because of record retention laws at the time. There is no open investigation into Dettmann with the department.

Police records do note that the sexual assault complaint was reported to the medical licensing board and that it was closed in 1986 after a consideration of the facts and a vote. The Wisconsin Department of Safety and Professional Services said it does not have records of closed complaints from that long ago.

Gaynor’s statement to the Journal Sentinel asserted that Dettmann was never sued, disciplined or investigated or had his licensure challenged, nor were any ethical complaints ever made against him.