Thank you two for your sincere responces, Philly and riverkid.
And I regret not having given a longer example sentence. Sorry about that.
Not to worry, Yoshio.
What I wanted
it to mean is as follows
A: When did you find that the man is innocent?
B: I found
that when I heard the account of an eyewitness. She seemed to be telling a lie.
I think that your dialogue would be more natural, Yoshio, if the 'finding out' was much more certain. "Find out" has a meaning of clearly discovering something. I think that the tentativeness [ "she seemed to be ...] makes it seem odd.
I also feel that the verb needed in this example dialogue is 'find something out' and the meaning is more like "I discovered that". [For the difference, see discussion below] Reporter: When did you discover [find out] that your client is innocent?
Private Detective: I found that out last week when his wife showed me a picture of them together at a restaurant in Hawaii. Pretty hard for a man to rob a bank when he's in Hawaii and the bank is in New York.
[OR, it could also be "I found out" with no 'that']
It seems to me "that" in this dialogue is similar to "that" used in riverkid's example so is it possible to use "I found that" in the above dialogue?
There's a difference in usage between "I found that" and "I found that out". Let me see if an example will suffice to show the difference.
A: Don always wants to have things done his way.
B: Yes, I've found that too. [= I realized that; I noticed that]
Sorry if the dialogue is not natural. I made up the dialogue.
It is often the case that an English word can be translated in many ways in Japanese and vice versa. And at that time I usually try to connect the meaning of the word to other English words, without thinking much about the use of them, I have to say.
I understand completely, Yoshio. I watched students struggle with this problem for many a year. Ganbatte!!