Earlier quoted context omitted.
I had the same feeling when I read how they told Mark to keep the laptop. I wish you guys all the best and hope this gets sorted out soon.
I get the whole leaving on good terms, really. But this whole "hey, we just want you to keep the code and answer questions for our other engineers" aspect really ought to have set off red flags. Pro-tip, hand write a nice letter to your boss/colleagues on your way out. Bingo, no burned bridges, and no risk of law suits for holding on to company IP.
It was Mark's manager John Shimmin who made that request. John is a great guy, and Mark had (still has?) a great relationship with him. He genuinely wanted to help Shimmin, and did so faithfully for weeks.
It's not fair to pin this on Mark and dismiss it with a "rookie move dude." Mark (and I) had no idea that facts could be twisted and ignored to create this kind of legal conflict. A lot of people operate under the guileless belief that if they help someone, that person/entity will not screw them. Mark is one of those people.