When Nate Roman came home from work on May 15, he could tell that a stranger had been in his house.

Roman, 44, lives in a single-family home on a typical suburban tree-lined street in Marlborough. He said it’s possible that he forgot to lock his back door, because whoever entered his house didn’t break anything to gain entry.

But here’s the strange part: whoever ventured into his home didn’t take anything. They just thoroughly cleaned his house.

Roman looked around and saw that they neatly made the beds, vacuumed the rugs, and scrubbed the toilets. They even crafted ornate origami roses on the toilet paper rolls in his bathrooms, he said. Every room in his house was cleaned, except for the kitchen.