The Police Did FemCon

The true terrorist organization behind the FemCon Incident was the Answell Police Department.

Reasons to suspect them

 * While it's unclear why, the murder of Kathryn Davies seems to hold some connection to FemCon. Joseph Pilfnam was the one who responded to Benjamin Mendax's call and could have easily manipulated with the crime scene, making it plausible that he is the one in charge of the terrorism.
 * Pilfnam appears in episode 4 and has his own theme that seemingly gives him a powerful presence. He is probably the culprit.
 * Answell Police Department has a long-standing history of corruption, according to Charlie Lawrence.
 * Their motive would be to eradicate their entire opposition so they can get away with arresting anyone they don't like.
 * They are the police, therefore they are the scum of the earth.

Concerns
As Storm and Lawrence survived the attack, they may wish death upon the two. Even if Pilfnam is co-operating with Lawrence, he may still betray him as he has his own ulterior motives.