As you may confronted some liars, you possibly would confirm that usually they forget what they have made-up and then related to you in the past and it's not unlekely that once they will forget in the future what they cited in the past.
I need an expression or possibly a proverb to explain the fact that usually all liars have a weak memory.
Example:
A) I tell you I couldn’t have done the murder, because I was up in London when it happened.
B) Which part of London?
A) Battersea.
B) Last time when I asked you, you said it was Bermondsey. Come on, let’s have the truth for a change. [The needed expression/proverb should come here.]
The only proverbial sentence I heard is:
All liar ought to have a good memory!
but I have no idea whether it works in current English or it's a Shakespearian wording of the statement in my question or what! Please let me know about it.
