Background check - failing submission of docs offer would stand revoked

I made couple of offers recently out of which one prospective is supposed to join us next week and in the mean time I 've started BG check and requested him to share the documents of all his 3 employers whom he claimed in resume .For past 2 days he is trying to confuse me saying different version of stories about hi past employers and finally failed to submit 2 ex employers relieving documents which he is not having .

Some how i tried reaching the Hr's of 2 companies they 've told me check with the candidate if he has completed exit formalities or not.Same has been questioned to him ..end up hearing some more stories.My question is how to address him saying that failing of submission of docs is not acceptable and offer 'ld stand revoke.Is it right doing? coz he has put down his papers already with his current employer based on our offer.

Note: In our offer letter we 've never mentioned about BG check and is it right to do BG with curent employer before some one accepts our offer.

He has not joined in your company and not worked even for a day. So you can terminate his offer.
When the candidate is failed in his background verification and he could not substantiate his whatever experience he had claimed, then you can consider him as a less experienced candidate. So he has to join for less salary than was proposed in the offer letter.
So you have give two options. one is on humanitarian grounds by considering him as less experienced person and pay him less salary. He can reclaim the original offer by producing his experience certificates in future.
Or
Due to his false claims in his resume which was proven, you can terminate his offer.