The cause of death, so far as is known, was never established.

They found that the cause of death could not be established.

The cause of death has not been established, his family said yesterday.

It can also be difficult to establish cause and effect.

The company said last night that the cause of the accident had not been established.

But as I said, the cause of this disaster has not yet been established.

The cause of the explosion has not been clearly established to this day.

The cause was never established and no one has ever been charged with his killing.

Neither the man's identity nor the cause of his death could be immediately established.

After the cause of the accident was established, they were dismissed.