Deciding the grammar 2

This question was found after giving some thoughts for "Deciding the grammar".

Which of the following sentence you think is correct?
A) Mac, did you know that the guy who just stared at you is your father?
B) Mac, did you know that the guy who just stared at you was your father?

For me, I would choose sentence A if I were to speak the above sentence. I think 'is' is used for sentence A because the guy is still Mac father is a eternal truth that can't be changed. However, I don't know if sentence B can be used.



Things got complicated when I gave the above sentence another thought where the above sentence is indicating event happened in the past like follow:

C) Prosecutor: Mr. Gilbert, did you know that the bank manager is your father, who had been missing for 15 years, before you went to the bank?
D) Prosecutor: Mr. Gilbert, did you know that the bank manager was your father, who had been missing for 15 years, before you went to the bank?

I don't know which one to choose, whether C or D, after trying to use the 'ethernal truth' concept I deducted from A and B and applied in on C and D. If you were the prosecutor, which sentence would you use?

Would you use "...is your father..." to indicate that the bank manager is Gilbert's father is an ethernal fact or would you use "...was your father..." to indicated who the bank manager really was at the time the event happened?

My concept about grammar usage is in chaos state now and I hope somebody could clear me up with how grammar works for above cases. I even think that there might be chances that C and D are both correct.