The father says that Nick just let a stranger borrow not only his computer but also his password.
...or maybe "someone" was already watching Moussoui & Nick offered the computer & password as a way of tracking what Moussoui said. The blame by the father may be because he suspected Nick was working for the government & was killed because of his "job."
I don't know, I have been pretty well convinced by my own intuition and comments here that the government wouldn't send a Jewish man with a passport with an Israel stamp to wander through Iraq.