"I happened to look outside and there was a woman walking down the road with my snowman," he told WISN-TV.
It wasn't the entire snowman, however -- the woman was carrying just the head.
Harper went outside and confronted the woman, who was with two other people.
"I was like so, 'are you going to bring that back or are you taking that as a souvenir?'" Harper told WDJT-TV.
The woman apologized and put the snowman head down, according to a police report. When Harper asked if anyone in the group would pay for the damage, the man got confrontational.
Police responded and identified the trio as having been at a bar earlier in the night. Michael and Melisa Koehler and Sara Alswager were cited by South Milwaukee police for damage to property.
The case took a surprising turn when the three vandals later showed up at Harper's door.
"They came over the next morning, and they apologized, which I was kind of surprised about," he said. "And they gave us $50 to replace it."
Harper said he understands people make mistakes. He's since replaced the headless snowman with one that he hopes stays intact.