Wiktionary
leave no stone unturned
vb. 1 (context idiomatic English) To search thoroughly (for something), looking in every conceivable place. 2 (context idiomatic by extension English) To perform a task carefully and thoroughly, not missing any step.
WordNet
leave no stone unturned
v. search thoroughly and exhaustively; "The police left no stone unturned in looking for the President's murderer"