When confronted with evidence a person knows to be true, they tend to admit things. For example, I've never denied that the content of any of my emails where what was represented, although it would be easy for anyone to alter them without tracability of the alteration.
It takes a real hardened liar to be able to deny evidence you know to be true, without some coaching.
This is true. Even on reality TV shows, normal people won't just keep lying when it's obvious they've been caught.
It would take a bizarre person not to come clean.