YOU SAID:

I mean, he knew he was dead.

INTO JAPANESE

つまり、彼は彼が死んでいることを知っていました。

BACK INTO ENGLISH

In other words, he knew that he was dead.

INTO JAPANESE

言い換えれば、彼は自分が死んだことを知っていた。

BACK INTO ENGLISH

In other words, he knew that he was dead.