fine-tooth comb
noun uk/ˌfaɪn.tuːθ ˈkəʊm/ us/ˌfaɪn.tuːθ ˈkoʊm/
with a fine-tooth comb （检查或查看）仔细地，彻底地
If you go through something with a fine-tooth comb, you examine it in great detail and with great care.
We have gone through the evidence with a fine-tooth comb. 我们已经仔细地检查过证据。