I was just wondering why USCIS needs a Police certificate if they check your criminal history anyway? or are they just doing the FBI check on the US side?

I have my police certificate since almost 2 month now since I orderd it when I DCF filed, hope it doesn't take that long nomore otherwise I have to obtain a new one which takes 4 weeks.

Since the passing of the Adam Walsh Act, the USCitizen has to undergo an FBI check as it relates to crimes pertaining to the act.
The beneficiary has always needed one for each place where he/she lived for more than 6 months since turning, I think, 16 ---- excepting the US.
Hope this helps, L.

The US Government actually doesn't have access to crime databases in other countries. The certificate gives criminal background information that may not otherwise be available.

For instance, how would the US Goverment determine that my Chinese wife had no criminal record in China?