He just listened to evidence that the pres played a roll in Killing an ex pres, selling nerve gas to terrorists and not for nothing, threatning his wife if she exposed him.
I think taking him into custody immediatly so that he could not add to his resume of the day was pretty important.
By the way, three things made me think Jack was in for some trouble at the end...
1. He was smiling
2. He RAN up the stairs of the warehouse to get the phone call.
3. After being able to do everything with his cellphone but make toast, a call, out of the blue from his daughter is sent to a land line in an abandonned warehouse
He must have been overtired and in despirate need of a bathroom break after the day he had to not see that as a major clue to trouble