This question already has an answer here:
In this sentence, "I still wished I could have done more", why isn't it saying, "I still wished I could do more"?
Beauty and the Beast season 2 episode 16: http://www.springfieldspringfield.co.uk/view_episode_scripts.php?tv-show=beauty-and-the-beast-2012&episode=s02e16
You okay? Yeah. [sic]
I don't know, it's a little bittersweet, though.
Yes, we finally stopped Sam, but, I don't know, it feels a little hollow, don't you think? We broke up their secret society.
Just take a little bit of digging.
We can put them away for a long time.
Yeah, I still wished I could have done more, though.
That's the old you talking.
The one that used to take the law into his own hands.
I like the new you better.
Oh, you do, do you? Six years is a long time to hold onto all that pain and anger.
Can't even imagine.
I know the difference in meaning between 'could' and 'could have', but here, I can't seem to get the grammar.