In the United States, terrorism suspect Najibullah Zazi confessed to preparing explosives five months ago, for a bombing attack on New York City subways. Zazi was persuaded to confess when the FBI said they would arrest and prosecute his mother for immigration fraud (she claimed someone as her son, who was not, so the phony son could improve his immigration status.) Going after the family of suspected criminals is a common practice in many parts of the worlds. It's an ancient practice based on "group responsibility" (the clan or family is responsible for the crimes of all their members.) Group responsibility was, and is, often the only way to maintain public safety in parts of the world that cannot afford police and a justice system. But many countries, especially in the Middle East, that have police and courts, still use the technique, especially in the case of serious crimes (like terrorism). Often, this is not sufficient, as Islamic terrorists are on a Mission From God, and beyond mundane matter like family loyalty.
The technique is still used in the West, usually in cases where the suspect comes from a family that is heavily into criminal behavior. The cops just take a close look at the parents and siblings, and if some evidence is found, you make arrests and tell the main suspect that a confession might make charges against mom and dad go away. Sometimes, just the threat of looking into family activities will produce cooperation.
Najibullah Zazi was born in Afghanistan, but his family emigrated to the United States when he was 14. Zazi used the Internet, and local Islamic radicals, to connect with Islamic terrorists back in the Pakistani tribal territories. He travelled to Pakistan to learn how to make explosives and bombs, attending terrorist schools in the tribal territories. His father was also arrested, for attempting to conceal the terrorist activities of his son. Both his parents still face imprisonment and deportation if their son does not give up all he knows about Islamic terrorist activity he was involved in.