On July 24, Nissen, 39, and his partner-in-training received a dispatch call regarding a distressed female motorist, Barbie Henderson, who had pulled over on the side of a northbound Hillview, Kentucky, highway.
"All we knew from the dispatch call was that there was a woman who was crying and needed help in her car. She opened the door for us when we approached, and I could see she was visibly upset," he tells PEOPLE. "She let us know that her sister had passed away."
Henderson explained to Wave3 News that she was "upset, screaming and hollering," when she got the news of her sister's passing while she was driving, and it was her first reaction to call 911.
Nissen, a veteran cop of over 17 years, said he then asked the woman if he could sit with her.
"Out of safety, I asked if I could talk with her and see if I could get her cooled down a bit," he said. "I turned the air vents towards her – it was over 90 degrees that day – held her hand, and she cried on my shoulder. I had her take sips of water."
Nissen spent over an hour with Henderson in the car, calming her down and making arrangements for a nearby family member to pick her up.
"I wanted her treated the way I would want my family to be treated if they needed help," he said.
When Henderson's sister, Shonda Barlow Garner, arrived at the scene, she was so amazed by the officer's kindness that she took a photo of the two and sent it to the Hillview Kentucky Police Facebook Page.
"Officer Nissen was more than an officer yesterday. He was a person with a heart to understand this was a lady who just lost her sister and heard the news over the phone. From there on he took care of my sister … What an awesome guy!!!!" she wrote.
The photo has since received over 8,000 likes and 2,000 shares.
"I didn't know this story would take off," Nissen said. "I was just trying to show the officer I was training that some compassion can go a long way."