Could Have.
Could Have + Past Participle (V3).
"1. Used to show that something is or might be possible:
Don't worry - they could have just forgotten to call.
2. Used to show that you are annoyed that somebody did not do something:
They could have let me know they were going to be late!
# (Spoken) Used to say that you need or would like to have something:
Her hair could have done with a wash.
3. Used to indicate that something was a possibility in the past, although it did not actually happen.
He could have made a fortune as a lawyer.
He did not regret saying what he did but felt that he could have expressed it differently.
Somebody could have been killed.
I could have warned you if I had known where you were.
He could have escaped, but he chose to stand and fight.
4. Emphasizing Your Feelings: (Spoken) Used to emphasize how happy, angry etc. you are by saying how you want to express your feelings.
I was so angry I could have killed her.
I was so relieved I could have kissed them all.
[Could = Sometimes he irritates me so much I could scream.]
Idiot! You could have told me!
He could have written.
[Could = We've come to see you, so you could at least stand and greet us properly.]
# You use why couldn't in questions to express your surprise or annoyance that someone has not done something.
Why couldn't she have said something?"