I would think this would be common sense at any job - unless otherwise specified in your contract the work that you do for your employer belongs to your employer, full stop. According to the article he freely admits that what he took included proprietary code - that is theft.

Now, was Goldman reasonable here? No, we can probably all agree that Goldman and the government overstepped a lot of bounds chasing this guy down. That said, I don't think some form of prosecution was unreasonable.