There's some possibility that you violated federal law by intruding on his computer like that. In reality, there's nearly no chance of prosecution, but there is - both legally and practically - a fairly clear distinction between "I care about my father" and "I snoop on my father's business without his knowledge or consent." This is firmly on the latter side of that line.

No legal conclusions can be drawn from having a copy of the TOR client. There are plenty of non-criminal reasons to use it, ranging from simple privacy concerns to security research, formally or informally. That it can also be used to mask criminal activity is not enough to conclude that your father is engaged in criminal acts.

Confronting your father to ask will also tip your hand that you've been digging through his files. I'd suggest letting this go. If you can't, speak to a counsellor and share your concerns in that venue, instead.