Firas Press quotes Arabic Asharq Al Awsat (couldn't find the original) as saying that the Mabhouh assassins had an electronic device that jammed the hallway cameras at the Rotana hotel.
They quoted an unofficial Israeli source as saying that some 19 minutes of camera footage is missing, between 8:24 and 8:43 PM, when the actual assassination took place.
The source said that there is no way that the assassins left enough evidence to prove who did it.