Theirs is a natural response to the violent death of their child. I was of the same mind 7 years ago after the tragic death of my nearly 18-year-old son. Even though his death was entirely of his own making (suicide), I eagerly blamed others. Why?
It is very difficult to accept that the dead are anything but innocent victims. You desperately do not want to blame your own flesh and blood for any part of the tragedy.
If you can, you want your dead child to be seen as some sort of hero, even if it is only by yourself.
You want to blame and punish a force that you see as much more powerful and unfeeling. Since the killers don't have a readily identifiable front, you go by default to some more easily recognizable entity. In this case, the FBI. They fit the bill nicely in that they are well-known, powerful, had contact with the victim, and had the power to forcibly remove him from the danger.
The young man who was murdered appears to have made some bad decisions. Hedecided to go looking for work in Baghdad. He drew too much attention to himself. He was a Jew. He didn't take good advice to leave.
Don't get me wrong. His death is a tragedy for his loved ones. He did not deserve to be murdered. He made some bad decisions.
Respectfully,
Mahatma