He knew its cause, but found no help in the knowledge.

However, she does not know the cause of his death.

Also no one knows the cause of the death which was most likely old age.

These two conditions are similar, and no one knows their cause.

She did not know the specific cause of the change.

Scientists do not yet know the cause of the recent change.

But he knew the cause of it: she was late.

Steel company officials said they did not know the cause.

Next: Do you know the specific cause of my pain?

It seemed she didn't know the cause, then, only the effect.