Falling Man by Don DeLillo is a story of living through and then coping with the aftermath of the terrorist attacks on the towers in New York on September 11, 2001. The two main characters are Keith, who was in one of the towers and survived, and his wife Lianne. Connected to Lianne are her mother Nina and her mother's long-time lover Martin.
Martin is a German art dealer with a somewhat secretive past, but here is what we know: his real name is Ernst Hechinger and he was once part of a terrorist movement in Germany. Though he was not one of the nineteen members of the group who were wanted for bombings, bank robberies, and murder, it is likely he was ancillary to them, perhaps part of a sleeper cell which supported their activities.
This history shapes Martin's view of the Islamic terrorists, and it is not surprising that he is sympathetic to their cause. Though he probably does not condone their acts, he does understand their frustration, their desire to make a statement, and their view of Americans as careless, hedonistic people. He tells Nina in an argument that these men kill and then people actually try to understand them, may even get to know their names, but they had to kill to get their attention. Martin also talks about their commitment to their god as being equal to anyone else's commitment to theirs.
Not too long after the incident, Martin and Nina separate after twenty years and travels across many continents. It was Martin's sympathy toward the terrorists which was responsible for ending the relationship.