No Witness Left

A tough bank robber barged into a bank and yelled loudly with a raised gun,
"This is a bank robbery, everybody surrender”. He quickly rounded up all the customers along with wetpant
bank guard together, then rushed to the teller and asked her to fill up his bag with money, which she did.
He then turned to a shivering rounded up customer and asked, "Did you see me rob this bank?"
The customer thought truth always wins, so he said, ""Yes sir, I saw you rob this bank."
The robber fired the gun and bang, shot the man dead.
Then he turned to a shivering couple and asked the husband, "Did you see me rob this bank?"
The man replied, "No, no, no, sir I did not, but this my wife, she sure did."