Screening Refugees

We will be hearing much in the coming weeks about the necessity to screen Syrian refugees. 

As someone who has worked with employers on hiring and screening procedures for years I have a basic and sincere question: 

Since refugees rarely arrive with solid documentation and reliable or even accessible references, how are they screened?

I haven't heard an answer that goes into the process. All answers I've heard go to the result, e.g. "They need to be carefully screened."

Exactly how is that going to be done? Who will do it? How long will that take?