background checks and documentation

[khurramc]

I wanted to question whether there is an actual verification process.

how do you check if the non-resident spouse is already married to another person or not before processing his application for green card?

can he simply get married to a US citizen and not tell the authorities that he is already married to someone else in his home country?

also, if he gets a divorce in his home country and is getting married to an american citizen, then what paper work is required?

would appreciate a response on this.

thanks.