Must Have + Past Participle (V3).

“1. You use must have to indicate that you are fairly sure that something is the case.

I must have been a bore.
She must have had a heart attack.
She must have put his clothes in the closet.

2. Used to say that something is likely or logical:

He must have known (= surely he knew) what she wanted. 
I'm sorry she's not here. She must have left already (= that must be the explanation).
In order to take that job, you must have left another job.

3. Used to say that you are certain about something. 

Your trip must have been fun!
It must have been very interesting for you.
Viewers must have been surprised.
You must have been really upset.
I must have made a mistake.”