Should I use "could be" or "could have been" in past-tense narration?

Question

Examples:

Using "could":

I looked at the flyer again, and then back at Mark. Very strange---meeting someone who didn't see me as a weirdo. But could it be true? Could there be a club dedicated to black magic?

using "could have":

I looked down at the glass table, an onset of tears stinging my eyes. Could Tom's mother have been right? Could I have been the one responsible for his death?

"Could" is the past of "can", but a the same time it can be used to indicate possibility (in the present tense). So, should I use "could be" or "could have been"?

Answer 1

"Could" in the first one is just the past tense of "can," as you correctly note.

In the second example, you are referring to a possibility in the "farther back" past. "Could Tom's mother have been right?" means that you have the present when the story is taking place (even though it's in the past tense) and some incident in the past (Tom's mother accused the narrator of being responsible for Tom's death).

If Tom's mother is standing in front of the narrator right now, then it would be "Could Tom's mother be right? Could I be the one responsible?"

So both your examples are correct, if the incident with Tom's mother happened at a previous point from the existing scene.