Here's my bet. I bet Casey convinced Lee that the cops were going to "pin this" on her and asked him to help her by doing something with her computer, erasing things, maybe he faked those emails about her imaginary job, etc. Lee, who impresses me a big doofus who thinks he's smart, did it for her.
He reminds me of Jethro Bodine,
, and I bet he thought he'd be a "double agent" and act like he was working "with" the cops, offered to "help" but all the while he'd be trying to ascertain what they had on Casey and where they were going with things, maybe also feeding more phony stuff to them. In the course of that, I bet he lied outright to them and that's another thing he's in trouble for. Betcha. Now of course he will say that he was only doing it because he thought they were framing her and that she never confessed anything to him, which may be true and which would explain his attorney saying "unknowingly" when describing anything Lee did.
Now, maybe the DA wants his testimony to show that Casey was manipulating her brother to lie and destroy evidence (computer) for her, which is of course an indication of guilt. They're pressuring him with the possibility of criminal charges because his testimony will help them convict her.
He reminds me of Jethro Bodine,

Now, maybe the DA wants his testimony to show that Casey was manipulating her brother to lie and destroy evidence (computer) for her, which is of course an indication of guilt. They're pressuring him with the possibility of criminal charges because his testimony will help them convict her.