Stone Unturned Leave Search Loop Boss Called Employees

1. The boss called the employees together for a meeting. He said he didn’t know who was stealing from the company, but that he would leave no stone unturned until he found out who it was.
2. The police looked everywhere for the prisoner who had escaped. They left no stone unturned, but they were unable to find him.

Synonym: beat the bushes

The expression suggests that whatever one is searching for might be under a stone, and that one will search so thoroughly as to turn over every stone looking for it.