A week ago there were rumors of Hammad being an Israeli "collaborator" and that he had fled to Israel, and Hamas denied those rumors.
Yet he has not been seen since then, and the rumors are growing stronger.
The Gaza interior ministry is responsible for all internal security, and most of the police in Gaza are also members of terror groups.
The current rumor is that the Qassam Brigades are engaging in a purge of the "old guard" of Hamas, having already executed former Hamas spokesman Ayman Taha fr being a spy for Egypt. Supposedly, they have detained Hammad after they arrested a female relative of his, Fahima Hammad. Fathi may have fled to avoid being targeted.
Hamas' chief bombmaker in the 1990s, Yahya Ayyash ("The Engineer"), was killed by Israel while at the home of another Hammad relative, Osama Hammad, causing more suspicion.
Apparently, Hamas has been very spooked by intelligence leaks, especially the one that led to the bombing of the home where the family of Qassam Brigades head Mohammed Deif were hiding. One rumor says that Hamas political bureau member Imad al-Alami was severely beaten and thrown out a second-story window by fellow Hamas members who suspected him of espionage.
Another rumor says that Hamas was displeased with Hammad for giving the orders to fire rockets during the cease-fire, causing Israeli retaliation and targeting of Deif, whose fate is still unknown.