priority for federal investigators, finding then scrubbing all of the electronic and social media communication that the san bernardino suspects may have utilized. >> we are going through a very large volume of electronic evidence. this is electronic evidence that these killers tried to destroy and tried to conceal from us. >> reporter: suspect tashfeen malik used a private facebook message to pledge allegiance to isis, but it's likely no one noticed because it was private. isis has become fluent in social media. in just one day last year, it posted 40,000 tweets. posting of the brutality. and recruiting new members. through an exploding digital community that offers secret communications with the ability to permanently delete. >> technology moves much faster than law enforcement so we have countless applications being created on a regular basis. all of them more -- more conducive to being secretive. >> reporter: in san bernardino the fbi will look for anything