Hamas needs to shoot someone, so it shoots its own people.
A few things to remember...
1. Collaboration is a blank check for executing anyone at any time without trial. Fatah and Hamas terrorists accuse each other of it. Like blasphemy charges, it's often a way of settling unrelated personal scores.
2. Hamas responds to each war by shooting a whole bunch of "collaborators". If terrorists can't kill enough Israelis, they can always inflate their kill count by killing their own people.
During ceasefires, it's not supposed to shoot Israelis. But it needs to shoot someone, so it shoots its own people.
4. Hamas is now arresting Gaza women on charges of collaboration. (via Khaled Abu Toameh)
The women were supposedly looking for information on children working with Hamas. Most of the evidence appears to come from their interactions with families of Hamas members. (See 1. Collaboration charges are usually a way to settle personal scores.)