Thad's read every entry, every message back to back that Nora has written in the journal.  Already knowing how to read the time lanaguge.

One of the only ones to deceiver it without technology or help.

It's his secretive way of feeling close to Nora, to his mother and it's peaceful for him. But when she stopped sending information to Eobarb he still wanted to read them, to know her a little more and be kept up to date with every action. 

So he caused a distraction for her and snatched it. He's so lost looking it he doesn't notice anyone else enter the room or stare at him. He just kept reading and feeling truly happy.  Enough to have tears of joy and a genuine smile until he noticed somebody had been watching him the whole time.

" I just wanted to be kept up to date about what's been going on. About her, it's my method of feeling....feeling close.  It doesn't concern you. Let me finish this and I'll return it to West-Allen." He says bitterly. " She will have no idea it was even missing. I don't leave traces.. Or proof I was there. "