Might Have + Past Participle (V3).

"1. Used when showing that something is or was possible:

The pills might have helped him.

2. Used to show that you are annoyed about something that somebody could have done:

Honestly, you might have told me!

3. Used to say that you are not surprised by something:

I might have guessed it was you!

4. Used to indicate that it is possible that something happened or was true, or when giving a possible explanation for something.

I heard what might have been an explosion.
She thought the shooting might have been an accident.

[might have = could have]

5. Used to indicate that something was a possibility in the past, although it did not actually happen.

Had the bomb dropped over a populated area of the city, there might have been a great deal of damage.

6. Used in expressions such as I might have known and I might have guessed to indicate that you are not surprised at a situation or a disappointing event or fact.

I might have known it was you!
I detest clutter, you know; I didn't know, but I might have guessed.
I might have guessed I'd get no sympathy from my family.

7. Indicating unrealized possibility:

I might have been killed!

8. Possibility: there is a possibility that it may happen or may be true, but you are not at all certain.

I suppose he might have missed the train.
I thought they might have gone home.

9. Somebody Should Have Done Something: used when you are annoyed because someone has not done something that you think they should do.

They might have cleaned up before they left.