From the New York Post:
It took a stranger from across the Atlantic to save the life of 9/11 hero and retired NYPD Detective John Walcott. Walcott, 43, who was stricken with leukemia in May 2003, had received an NYPD line-of-duty disability pension for his 9/11 rescue and recovery work. But it was Olaf Gierszewski, now 38, a petty officer in the German Navy, who came to Walcott's rescue in an unusual international stem-cell transplant...
After a shipmate took ill in 1999, Gierszewski signed up with the German DKMS, the Bone Marrow Donor Center, which has a registry of 1.6 million possible donors. The group has a Manhattan-based branch, DKMS Americas. But it wasn't until October 2003 that the sailor got a call from his commanding officer, who told him, "Somebody is sick. You seem to be a match."
Without hesitation, Gierszewski underwent a five-hour procedure to extract his blood and run it through a machine that removes white cells. Those cells were jetted to America and given to Walcott in a blood transfusion after his chemotherapy. With the one-in-a-million match, Walcott, who lives in Rockland County, was given new hope to live.
Gierszewski's stem cells "acted like a Pac-Man to kill any remaining cancer cells and jump-start my own cells," said Walcott, the father of a 5-year-old girl. His leukemia has remained in remission since.