BEDFORD, N.H. - Bedford Police Officer Michael Cherwin is used to answering the call for help. He's been on the job for 12 years.
In 2013, he took part in a bone marrow test set up by a fellow officer.
"[It was a] quick, easy process -- just a swab of the cheek," Cherwin explained.
At the time, officer Cherwin didn't think too much more about it. That was until the spring of this year when he got an email related to that swab six years ago.
At first, he didn't believe it.
"It was saying that I was a match. A possible match for somebody," he said.
Cherwin wasn't just a match, he was a perfect match.
"They called me that night and they asked if I wanted to go through with it and I said, 'absolutely.' I didn't think twice about it," he said.
Cherwin took 30 hours of his personal time to go through the process, helping a complete stranger -- a cancer patient in need of his marrow.
Pictures from the hospital show him preparing for the procedure. The actual donation surgery took 4-6 hours.
Cherwin still knows nothing about the recipient but hopes to one day learn more.
"It's just the right thing to do. I figured if I need the help, I would hope that somebody would do the same thing for me," he said.
He used DKMS.org, where you register online.
They send you a kit to take your swab and then send it back and you wait.
Officer Cherwin hopes others will do the same thing and potentially save a life.
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