Chris Long is an IT worker in the Washoe County Sheriff’s Department in Reno, Nevada. But all the DNA in his semen belongs to a German man he’s never met.

That’s because Long received a bone marrow transplant from the European stranger four years ago — and the unexpected impact it has had on his biology could affect the future of forensic science.

According to a newly published New York Times story, the purpose of the transplant was to treat Long’s acute myeloid leukemia, a type of cancer that prevents the body from producing blood normally.