Why did he return 1000btc to theymos instead of running away with it?

So that he would seem trustworthy. Or perhaps because he is/was trustworthy. Really, we are only guessing, since there is no good way to know for sure.
Why didn't he return all the other bitcoin he held in escrow?

Because he died? Or because he is a scammer? Or because something in his life has interfered with his ability to do so? Really, we are only guessing, since there is no good way to know for sure.
I've heard many people saying that "he is holding many other people's BTC in escrow", but I haven't heard anyone specifically say that he is holding
their bitcoins. Is there a reliable source of information about which escrows he is still holding?