There are still unanswered questions following the December terrorist incident in San Bernardino, Ca. Authorities still are uncertain whether Syed Rizwan Farook had assistance from foreign terror groups or if he planned other attacks. Was he a lone wolf terrorist?
What is not still in doubt is that Farook committed an act of terror and U.S. law prevents people from profiting from terrorist acts. Because of that, the federal government has filed a lawsuit to seize the life insurance benefits from two policies Farook took out as reported by Fox News in "US seeks to seize San Bernardino shooter's life insurance." Farook's mother was the beneficiary of both policies.
Currently, it is unknown whether the shooters had estate plans and, if they did, who their heirs would be. However, it is certain that whoever ends up inheriting their estates will not likely keep very much of it, if they are even able to keep any of it.
The families of the victims will most likely sue the estates for any assets. Although there is unlikely to be very many assets in the estates, it can be an important symbolic message to go after what is there and it may help the victims' families get closure.
Reference: Fox News (June 1, 2016) "US seeks to seize San Bernardino shooter's life insurance."