The anti-Hamas Palestinian Press Agency is reproducing a letter, allegedly from al-Qassam Brigades leader Ahmed Jabari to Khaled Meshal, Hamas' "political" leader in Damascus. The letter details the security chaos in the Gaza Strip and indicates that Hamas may be losing its grip on power. The implication is that some of the recent "work accidents" might have actually been murders of Hamas members.
I cannot auto-translate the letter itself because it is not in text format; if anyone out there knows Arabic and wants to give it a shot, please do so. Page 2 does seem to list specific events that would prove the point, though.