The peasants were looking for antiquities to sell. They broke into the coffins, and then they destroyed the bodies.
6 seconds sound clip from the Isle of the Dead (1945) movie soundboard.
You can hear this line at 00:09:52.325 in the Blu-ray version of the movie.
Quote context
[...]
- General Pherides. I am honored, sir. Please, won't you come in?
- I came here to visit the last resting place of my wife.
- I found the coffins broken, empty, all of them.
- I'm extremely sorry, General. It happened a long time ago.
- Has anyone been punished for this crime?
- You see, I am an archaeologist. And this island was the great find of my life.
- Such treasures. Antiquities dating back to Homer. But I paid for them with my uneasy conscience.
- Unwittingly I have turned good, simple people into grave robbers. The fault is mine.
- The legal guilt is theirs and must be reported to the authorities.
[...]