The technician suspected a dead animal inside the wall. After finding a small opening near the baseboard and seeing insects around it, he opened part of the wall to investigate.
Instead of one dead animal, dozens of cockroaches poured out. Further inspection revealed thousands of them living inside the wall, along with droppings, egg cases, shed skins, and dead insects.
The odor was coming from the massive infestation and accumulated waste. After several treatments, cleaning, and sealing the entry points, the smell finally disappeared.
